(Reuters) - Islamic State fighters seized more than a third of the Syrian border town of Kobani, a monitoring group said on Thursday, as U.S.-led air strikes failed to halt their advance and Turkish forces looked on without intervening.

With Washington ruling out a ground operation in Syria, Turkey said it was unrealistic to expect it to mount a cross-border operation alone to relieve the mainly Kurdish town.

The U.S. military said Kurdish forces appeared to be holding out in the town, which lies within sight of Turkish territory, following fresh airstrikes in the area against a militant training camp and fighters.

However, the Syrian Observatory for Human Rights said Islamic State, still widely known by its former acronym of ISIS, had pushed forward on Thursday.

"ISIS control more than a third of Kobani - all eastern areas, a small part of the northeast and an area in the southeast," said Rami Abdulrahman, head of the Observatory, which monitors the Syrian civil war.

The commander of Kobani's heavily outgunned Kurdish defenders confirmed that the militants had made major gains, after a three-week battle that has also caused the worst street clashes in years between Turkish police and Kurdish protesters.

Militia chief Esmat al-Sheikh put the area controlled by Islamic State, which controls large amounts of territory in Syria and neighbouring Iraq, at about a quarter of the town. "The clashes are ongoing - street battles," he said by telephone from the town.

Explosions rocked Kobani throughout the day, with black smoke visible from the Turkish border a few kilometres (miles) away. Islamic State hoisted its black flag in the town overnight and a stray projectile landed 3 km (2 miles) inside Turkey.

The town's defenders say the United States is giving only token support with its air strikes, while Turkish tanks sent to the frontier look on but do nothing to defend the town, where the United Nations says only a few hundred remain. Over 180,000 people from the city and surrounding area have fled into Turkey.

U.S. Central Command said it had conducted five strikes near Kobani on Wednesday and Thursday, and that Kurdish forces still appeared to control most of the town.

The strikes damaged an Islamic State training camp and destroyed a support building, as well as hitting one small unit and one large unit of militant fighters, Centcom said.

UNREALISTIC EXPECTATIONS

Turkey's foreign minister, Mevlut Cavusoglu, played down the chances of its forces going to the aid of Kobani.

"It is not realistic to expect Turkey to conduct a ground operation on its own," he told a joint news conference with visiting NATO chief Jens Stoltenberg. However, he added: "We are holding talks ... Once there is a common decision, Turkey will not hold back from playing its part."

Ankara resents suggestions from Washington that it is not pulling its weight, and wants broader joint action that also targets the forces of Syrian President Bashar al-Assad. "We strongly reject allegations of Turkish responsibility for the ISIS advance," said a senior Ankara government source.

"Our allies, especially the U.S. administration, dragged their feet for a very long time before deciding to take action against the catastrophic events happening in Syria," he added.

Turkey has long advocated action against Assad during the civil war, which grew out of a popular uprising in 2011. However, the United States called off air strikes on Damascus government forces at the last minute last year when Assad agreed to give up his chemical weapons. It has also managed so far to fly sorties across Syria with tacit consent from Assad.

Kerry, too, played down Kobani's significance as a pointer to U.S. policy, and said other towns might also be vulnerable to Islamic State as the U.S.-led efforts in the region would take "weeks and months" to play out.

"Kobani is a tragedy because it represents the evil of ISIS, but it is not the definition either of the strategy or the full measure of what is happening with response to ISIS," he told reporters in Boston.

"We are only a few weeks into building the coalition," Kerry said. "The primary goal of this effort has been to provide the space for Iraq to be able to get its government in place and to be begin to push back and to begin to be able to deprive them (Islamic State militants) of their command and control, their supply centres and their training. That is taking place."

Retired U.S. General John Allen, asked by President Barack Obama to oversee the creation and work of the anti-Islamic State coalition, was in Ankara on Thursday for two days of talks with Turkey's leaders.

President Tayyip Erdogan wants the U.S.-led alliance to enforce a "no-fly zone" to prevent Assad's air force flying over Syrian territory near the Turkish border, and to create a safe area for around 1.5 million Syrian refugees in Turkey to return.

Stoltenberg said neither had been discussed by NATO.

TURKISH CLASHES

The anger felt by Turkey's Kurds over Ankara's failure to help their brethren in Syria threatens to unravel a fragile peace process that Erdogan hoped would end a 30-year armed struggle for autonomy by the Kurdistan Workers' Party (PKK).

At least 25 people died in the mainly Kurdish southeast of Turkey on Wednesday during clashes between security forces and Kurds demanding that the government do more to help Kobani.

On Thursday, gunmen wounded a police officer in an attack on a police station in Turkey's southeastern province of Siirt, where five people died during earlier protests. There were also clashes in Istanbul and Ankara.

Wednesday's violence prompted curfews to be imposed in five southeastern provinces, restrictions unseen since the height of the PKK's war against Turkish forces in the 1990s, and streets were calmer as a result.

Erdogan said protesters had exploited the events in Kobani as an excuse to sabotage the peace process.

Selahattin Demirtas, head of the Kurdish People’s Democratic Party (HDP), which had urged Turkish Kurds to take to the streets this week, denied that this had provoked violence. He appealed for calm and said jailed PKK leader Abdullah Ocalan had called for talks with the government to be stepped up.

Kurdish leaders in Syria have asked Ankara, so far in vain, to establish a corridor through Turkey to allow aid and possibly arms and fighters to reach Kobani.

Ankara is suspicious of Syria's Kurds for having achieved self-rule by tacit agreement with Assad after he lost control of the region to anti-government rebels, and fears this could revive secessionist aspirations among its own Kurds.

Turkish police fired tear gas against Kurdish protesters in the town of Suruc near the border overnight, and the shutters of most shops were kept shut in a traditional mark of protest.

Ferdi, a 21-year-old Turkish Kurd watching the smoke rising from Kobani, said if the town fell, the conflict would spread to Turkey. "In fact," he said, "it already has spread here."

(Reuters) - At least 21 people were killed in riots across Turkey, the deadliest street unrest in years, after the Kurdish minority rose up in fury at the government's refusal to protect a besieged Syrian town from Islamic State.

Street battles raged between Kurdish protesters and police across Turkey's mainly Kurdish southeast, in Istanbul and in Ankara, as the fallout from war in Syria and Iraq threatened to unravel the NATO member's own delicate peace process with Kurds.

Across the frontier, U.S.-led air strikes appeared to have pushed Islamic State insurgents back to the edges of the Syrian Kurdish border town of Kobani, which the militants had been poised to capture this week after a three-week siege.

Washington said its war planes, along with those of coalition ally the United Arab Emirates, had struck nine targets in Syria, including six near Kobani that hit Islamic State artillery and armored vehicles. It also struck Islamic State positions in Iraq five times.

Nevertheless, Kobani remained under intense bombardment from Islamic State emplacements, within sight of Turkish tanks that have so far done nothing to help.

U.S. officials were quoted voicing impatience with the Turks for refusing to join the coalition against Islamic State fighters who have seized wide areas of Syria and Iraq. Turkey says it could join but only if Washington agrees to use force against Syrian President Bashar al-Assad as well as the Sunni Muslim jihadists fighting him in a three-year-old civil war.

Turkey's own Kurds, who make up the majority in the southeast of the country, say that President Tayyip Erdogan is stalling while their brethren are killed in Kobani.

Police fired tear gas and water cannon to disperse demonstrators who burned cars and tires. Authorities imposed curfews in at least five provinces, the first time such measures have been used widely since the early 1990s.

Turkish Prime Minister Ahmet Davutoglu told reporters in Ankara that 19 people were killed and 145 wounded in riots across Turkey, vowing that Turkey's own peace process with Kurdish separatists would not be wrecked by "vandalism". Dogan news agency later said the death toll had climbed to 21. At least 10 people died in clashes in Diyarbakir, the largest Kurdish city in Turkey's southeast, according to Agriculture Minister Mehdi Eker, who said an all-day curfew imposed there from Tuesday night would be reviewed on Wednesday.

Pockets of protesters defying the curfew clashed with security forces there later on Wednesday, local media reported.

Others died in clashes between protesters and police in the eastern provinces of Mus, Siirt and Batman. Thirty people were wounded, including eight police officers, in Istanbul.

Disturbances spread to other countries with Kurdish and Turkish populations. Police in Germany said 14 people were hurt in clashes there between Kurds and radical Islamists.

The unrest in Turkey, which has NATO's second largest armed forces, exposes the difficulty Washington has faced in building a coalition to fight Islamic State in Syria and Iraq, two countries with complex, multi-sided civil wars in which every country in the region has a stake.

BLACK FLAG

Islamic State fighters besieging Kobani hoisted their black flag on the eastern edge of the town on Monday. Since then, U.S.-led air strikes have been redoubled, and the town's defenders say the insurgents have been pushed back.

Intense gunfire and loud explosions could be heard on Wednesday morning from across the Turkish frontier, and huge plumes of gray smoke and dust rose above the town, where the United Nations says only a few hundred inhabitants remain.

"They are now outside the entrances of the city of Kobani. The shelling and bombardment was very effective and as a result of it, IS (Islamic State) have been pushed from many positions," Idris Nassan, deputy foreign minister of the Kurdish-run Kobani district administration, told Reuters by phone.

"This is their biggest retreat since their entry into the city and we can consider this as the beginning of the countdown of their retreat from the area."

U.S. officials, acknowledging it will be difficult to shield Kobani from the air, have played down its strategic importance.

"People need to understand we need a little strategic patience here. This group is not going to go away tomorrow, and Kobani may fall. We can't predict whether it will or it won't," Pentagon spokesman Rear Admiral John Kirby said on CNN.

"There will be other towns that they will threaten, and there will be other towns that they will take. It is going to take a little bit of time."

Secretary of State John Kerry said: "As horrific as it is to watch in real time what is happening in Kobani ..., you have to step back and understand the strategic objective."

Islamic State has been advancing on the town from three sides and pounding it with artillery despite dogged resistance from heavily outgunned Kurdish forces.

Kurdish media said Kurdish fighters thwarted a car bomb on positions in Kobani, saying the vehicle blew up before reaching its target. An Islamic State source on Twitter said the attack destroyed a police station. Neither account could be verified but a huge explosion could be seen from across the border.

In Turkey, parliament voted last week to authorize cross-border intervention, but Erdogan and his government have so far held back, saying they will join military action only as part of an alliance that also confronts Assad.

Erdogan wants the alliance to enforce a "no-fly zone" to prevent Assad's air force flying over Syrian territory near the Turkish border and create a safe area for an estimated 1.2 million Syrian refugees in Turkey to return.

France said it supported the idea of a safe area, and Britain said it was studying it. But it is clear the proposal has not taken hold in Washington, which has been bombing Islamic State targets in Syria without Assad raising objections, and does not want to be dragged into a conflict against Damascus.

"At the moment, the American air force is flying all over Syria with the permission of the Assad government," said Tim Ripley, a defense expert for Jane's Defence Weekly.

"To try and impose a no-fly zone would potentially involve a major air war against one of the biggest air forces in the Middle East ... which would only be a distraction from the fight against (Islamic State)," he said.

Kerry, repeating lukewarm views of other U.S. officials, said: "The buffer zone is an idea that has been out there. It is worth examining, it's worth looking at very, very closely." Pentagon spokesman Kirby said: "It is now not on the table as a military option that we are considering."

U.S. IMPATIENCE

The conflict has already opened up a fissure in relations between the United States and Turkey, its most powerful ally in the area. U.S. Vice President Joe Biden was forced to apologize last week after Erdogan took umbrage at comments Biden made at Harvard University, in which he blamed Turkey's open borders for allowing Islamic State to bring in recruits.

An unnamed senior U.S. official told the New York Times on Tuesday there was "growing angst about Turkey dragging its feet to act to prevent a massacre less than a mile from its border".

"This isn’t how a NATO ally acts while hell is unfolding a stone's throw from their border," the official said.

Kerry said Turkey was still deciding what role it would play. Retired U.S. General John Allen, charged with building a coalition against Islamic State after it seized about a third of neighboring Iraq, is due in Turkey this week.

But, while taking in Kobani's refugees and treating its wounded, Turkey has deep reservations about deploying its own army in Syria. Beyond becoming a target for Islamic State, it fears being sucked into Syria's three-year-old civil war.

It also distrusts Syria's Kurds, allies of Turkey's own Kurdistan Workers' Party (PKK), which waged a decades-long insurgency for Kurdish autonomy in which around 40,000 people were killed.

The PKK's jailed leader, Abdullah Ocalan, has said any massacre of Kurds in Kobani would doom a fragile peace process with the Turkish authorities, one of the most important initiatives of Erdogan's decade in power.

The street protests across Turkey were already making the prospect of reconciliation with nationalists seem more remote, as protesters set fire to Turkish flags and attacked statues of the founder of modern Turkey, Mustafa Kemal Ataturk.

Selahattin Demirtas, co-chair of the HDP, Turkey's leading Kurdish party, condemned such acts as "provocations carried out to prevent help coming to the east (Kobani) from the west".

(Reuters) - The main Kurdish armed group in Syria called on its kinsmen across the region to help it stop a massacre in the Syrian town of Kobani as Islamic State militants armed with tanks edged closer on its outskirts and pummelled it with artillery fire.

Islamic State's battlefield gains in recent months have come as Syrian President Bashar al-Assad's forces have focussed on other rebel groups. On Friday the army advanced on the city of Aleppo further west, threatening rebel supply lines in a potentially major reversal.

U.S.-led forces have been bombing Islamic State targets in Syria and Iraq but the action has done little to stop the group's advance in northern Syria towards the Turkish border, piling pressure on Ankara to intervene.

Canada said it would send fighter jets and other aircraft to take part in the U.S.-led strikes on Islamic State in Iraq for a period of up to six months.

Turkey said it would do what it could to prevent Kobani, a predominantly Kurdish town just over its southern border, from falling into Islamic State. It has stopped short of committing to any direct military intervention and Syria warned on Friday against any Turkish "aggression" on its territory.

A statement issued by the YPG, the main Kurdish armed group, vowed "never ending" resistance to Islamic State in its advance on Kobani. "Every street and house will be a grave for them."

"Our call to all the young men and women of Kurdistan ... is to come to be part of this resistance."

DESTRUCTION

Esmat al-Sheikh, head of the Kurdish forces defending Kobani, said the distance between his fighters and the insurgents was now less than one kilometre (half a mile).

"We are in a small, besieged area. No reinforcements reached us and the borders are closed," he told Reuters by phone. "My expectation is for general killing, massacres and destruction."

Islamic State has carved out swathes of eastern Syria and western Iraq in a drive to create a caliphate between the Euphrates and the Tigris rivers. Kobani's resistance has prevented it from consolidating territory across Syria's north.

Fighting continued after the sun set, with artillery strikes on residential areas east and southwest of Kobani's centre. Kurds returned fire, and red tracer bullets targeting Islamic State strongholds east of the city flew over rooftops, a Reuters correspondent on the Turkish side of the border said.

Remzi Savas, 53, smoked a cigarette and listened to the gunfire over the border.

"My son is over there, he crossed through a minefield to get there. He is just 14. There are many children fighting for the YPG, we can't hold them back. They think they'll lose everything if Kobani falls."

The British-based Syrian Observatory for Human Rights said at least 80 shells had hit the town, known as Ayn al-Arab in Arabic, and there were heavy clashes in the east and southeast.

The fighting has driven Kurds from across northern Syria from their homes across the border into Turkey.

"It's a dramatic humanitarian tragedy as we have all witnessed," U.N. High Commissioner for Refugees Antonio Guterres said in Geneva. "It's the largest single outflow of Syrians in a few days, 160,000 people."

ALEPPO ENCIRCLED

Further west, a Syrian army advance threatened to take the last main rebel supply route leading into Aleppo from the north and reverse two years of gains by Assad's foes.

"They are going to encircle Aleppo," said Abu Abdo Salabman, a member of the political office of the Mujahideen Army, a rebel group viewed as part of the moderate opposition to Assad.

"They are bombing us non-stop," said Salabman, who was not using his real name. "They are marching on us and the regime air force is non-stop."

The Syrian army has taken control of three villages, state television said, in a campaign by Assad's forces that could encircle insurgents in the city.

Although there are smaller, more indirect routes into Aleppo, taking the northern road would also allow the army to besiege areas of the city which fell to insurgents in 2011, a tactic it used to retake Homs city in May.

Assad's forces are fighting a mixture of rebel groups in Syria, including Islamic State but also a mix of western-backed forces in a conflict which has killed nearly 200,000 people.

This year, Washington and its allies have shifted focus in Syria from battling Assad to combating Islamic State.

The U.S. military said coalition forces carried out strikes in Iraq and Syria overnight on Thursday. In Syria they destroyed an Islamic State garrison, two of the militant group's tanks and hit two mobile oil refineries and a training camp.

In Iraq, government forces recaptured the town of Dhuluiya, about 70 km (45 miles) north of Baghdad, which had been under siege by Islamic State.

Prime Minister Haider al-Abadi called on Iraq's bickering political factions to unite. In a message to mark the Muslim holy feast of Eid, he said the battle against Islamic State would continue to the end.

TURKISH DILEMMA

Village by village, Kurdish forces in northern Iraq have regained around half the territory they gave up in August when Islamic State militants tore through their defences in the northwest, prompting the United States to launch air strikes in September, its first since 2011.

Turkey, however, insists the air strikes alone will not contain the Islamic State threat, and wants simultaneous action to be taken against Assad's government, including the creation of a no-fly zone on the Syrian side of the border.

Prime Minister Ahmet Davutoglu said Turkey would do what it could to prevent Kobani from falling to the militants but stopped short of committing to the sort of intervention Kurds have called for.

"We wouldn't want Kobani to fall. We'll do whatever we can to prevent this from happening," Davutoglu said in a discussion with journalists broadcast on the A Haber television station.

Parliament gave the government powers on Thursday to order cross-border military incursions against Islamic State, and to allow forces of the U.S.-led foreign coalition to launch similar operations from Turkish territory.

Syria said Turkey's decision was an act of aggression which could have "catastrophic consequences".

But Davutoglu appeared to pull back from any suggestion that Turkey was planning a military incursion, saying this could drag Ankara into a wider conflict along its 900 km (560-mile) border.

Ankara fears intervention could worsen security on its border by strengthening Assad and bolstering Kurdish fighters linked to the Kurdistan Workers Party (PKK), which has waged a three-decade insurgency against the Turkish state.

(Reuters) - A Twitter account run by an Qaeda member said the leader of the al Qaeda-linked Khorasan group was killed in a U.S. air strike in Syria, SITE monitoring service said on Sunday, following several days of uncertainty over whether he survived the raid.

A U.S. official on Sept. 24 said the United States believed Mohsin al-Fadhli, a senior al Qaeda operative, had been killed in a strike a day earlier, but the Pentagon said several hours later that it was still investigating what had happened to him.

In a message posted on Sept. 27, the jihadist offered condolences for the death of Kuwaiti-born Fadhli, otherwise known as Abu Asmaa al-Kuwati or Abu Asmaa al-Jazrawi, following the Sept. 23 air strike, SITE reported.

U.S. officials have described Khorasan as a network of seasoned al Qaeda fighters with battlefield experience mostly in Pakistan and Afghanistan that is now working in league with al Qaeda’s Syrian affiliate, the Nusra Front.

Khorasan is a term for an area including parts of Pakistan and Afghanistan where al Qaeda’s main council is believed to be in hiding.

After the Sept. 23 strikes, U.S. officials said they were was still assessing how badly Khorasan had been hit. Islamist militants on social media have said there were unconfirmed reports that the 33-year-old Fadhli had been killed.

SITE did not name the jihadist who reported Fadhli's death but said he had trained under a close associate of al Qaeda leader Ayman al-Zawahri and had fought in Khorasan before traveling to Syria.

A 2012 State Department notice offering a $7 million reward for information on Fadhli's whereabouts said he was an al Qaeda financier close to al Qaeda founder Osama bin Laden and among the few who knew in advance about the Sept. 11, 2001, attacks.