(Reuters) - A suicide bomber detonated his explosives belt in a market north of Baghdad on Saturday, killing 11 people and wounding 21 others, medical and police officials said.

The attack took place about 28 km (17 miles) north of the capital, between the towns of Tarmiyah and Mishahda. The area has been the scene of clashes between Iraqi forces and Islamic State (IS) fighters, who have taken control of large sections of northern and western Iraq this year.

In other violence, four Iraqi soldiers died in a friendly-fire incident in the town of Udaim, 90 km northeast of Baghdad.

The soldiers, who had been wounded by IS fighters, were being taken to hospital when Shi'ite militia volunteers who mistook them for insurgents fired a rocket-propelled grenade at their vehicle, police and medical officials said.

(Reuters) - The Iraq war veteran accused in the September 19 breach of the White House pleaded not guilty on Wednesday in federal court.

The court ordered a mental competency review for Omar Gonzalez, who suffers from post-traumatic stress disorder, but defense lawyers opposed the evaluation.

Gonzalez's lawyer, David Bos, said his client was mentally competent and did not need an evaluation. He said he has become increasingly confident in his client's competency.

Gonzalez was captured inside the White House on Sept. 19 with a knife after he jumped the fence at the presidential mansion, burst through the front door and ran about 130 feet (40 meters) into the East Room, used for events and receptions.

He was charged with unlawful entry while carrying a weapon. A federal grand jury indicted him on Tuesday on that federal offense, along with District of Columbia charges of carrying a dangerous weapon outside a home or business and unlawful possession of ammunition.

At a congressional hearing on Tuesday on the breach, lawmakers asked Secret Service Director Julia Pierson how Gonzalez escaped greater scrutiny.

In July, he was arrested in Virginia for reckless driving, eluding police and possessing a sawed-off shotgun. In August, he was stopped, but not arrested, while walking along the south fence of the White House with a hatchet in his waistband.

(Reuters) - Islamic State fighters tightened their siege of a town on Syria's border with Turkey on Friday despite U.S.-led air strikes aimed at defeating the militants in both Syria and Iraq, in a coalition which has now drawn widespread European support.

Washington's closest ally in the wars of the last decade joined the alliance at last on Friday after weeks of weighing its options: Britain's parliament voted 542 to 43 to back Prime Minister David Cameron's decision to join air strikes on Iraq.

Belgium's parliament also voted 114 to 2 on Friday to take part and Denmark said it would send planes. Six Belgian F-16s took off for a staging post in Greece even before the vote.

"This is not a threat on the far side of the world. Left unchecked, we will face a terrorist caliphate on the shores of the Mediterranean and bordering a NATO member, with a declared and proven intention to attack our country and our people," Cameron told British lawmakers.

Until this week France was the only Western country to answer President Barack Obama's call to join the U.S.-led campaign. Since Monday, Australia and the Netherlands have also joined. On Friday Germany expressed support for the mission despite saying it would not send aircraft of its own.

Obama has sought to rally international support for a military coalition against Islamic State, a powerful force in Syria which swept through much of northern Iraq in June, slaughtering prisoners and ordering Shi'ites and non-Muslims to convert or die.

The campaign has brought Washington back to the battlefield in Iraq that it left in 2011 and into Syria for the first time after avoiding involvement during a civil war that began the same year.

The coalition also includes several Arab states, all led by Sunni Muslims alarmed at the rise of Islamic State.

Islamic State has emerged as the most powerful Sunni militant group battling the Shi'ite-backed governments in Iraq and Syria. Its fighters are also battling against rival Sunni rebel groups in Syria and against Kurds in both Syria and Iraq, countries facing complex, multi-sided civil wars in which nearly every state in the Middle East has a stake.

French public support for the mission surged this week after the beheading of a French tourist in Algeria by captors who said it was retaliation for French participation in strikes in Iraq.

Paris said it might also join U.S. strikes in Syria although there was no plan yet to do so. European countries have so far agreed only to strike targets in Iraq, where the government has asked for help, and not in Syria, where President Bashar al-Assad has not given permission, although he has not objected.

The White House said it was pleased at the British decision and the pace at which the coalition was growing.

"WE'RE AFRAID"

More than a month since Washington began striking Islamic State targets in Iraq, and four days since it extended the campaign into Syria, there are signs fighters are lowering their profile in areas they control to become a harder target.

General Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, said this week's strikes in Syria had disrupted Islamic State's command, control and logistics capabilities.

But the air campaign has yet to halt the group's advance in Syria, where fighters have laid siege to a Kurdish town on the Turkish border, sending 140,000 refugees across the frontier since last week in the fastest exodus of the three-and-a-half-year-old civil war.

Some Kurdish commanders have said the air campaign has given the militants' advance greater impetus by prompting them to move armor out of positions in cities and send it to the front lines, where Western planes have yet to strike.

The main battle in northern Syria has been visible from across the border in Turkey. The boom of artillery and bursts of machinegun fire echoed across the area and at least two shells hit a vineyard on the Turkish side of the border, though there were no immediate reports of casualties inside Turkey.

"We're afraid. We're taking the car and leaving today," said vineyard owner Huseyin Turkmen, 60, as small arms fire rang out in the Syrian hills just to the south.

Islamic State fighters appeared to have taken control of a hill 10 km (6 miles) west of Kobani from where the YPG, the main Kurdish armed group in northern Syria, had been attacking them in recent days.

The British-based Syrian Observatory for Human Rights, which monitors the war, said Islamic State fighters had also taken control of a village around 7 km (4 miles) east of Kobani.

Kurdish forces said on Thursday they had pushed back the advance on Kobani, also known as Ayn al-Arab, but appealed for U.S.-led air strikes on the insurgents' tanks and heavy weapons.

"The clashes are moving between east, west and south of Kobani ... The three sides are active," Idris Nassan, deputy foreign minister in the area's Kurdish administration, said by phone from the center of the town.

"They are trying hard to reach Kobani. There is resistance here by YPG, by Kobani and some volunteers from north Kurdistan Turkish Kurds," he said. "Every girl, every young man, every man who is able to fight, to carry a gun, they are armed and they are ready to defend and fight."

NATO member Turkey has been conspicuously absent from the coalition against Islamic State, angering its Kurdish residents.

SYRIAN AIR STRIKES

The U.S. military said its planes blew up four Islamic State tanks in eastern Syria and hit a number of targets in Iraq.

The Syrian Observatory monitoring group said one U.S.-led strike in eastern Syria had killed an "important" Islamic State figure on a motorbike. It did not identify the victim.

Assad's Syrian government has not objected to the U.S.-led campaign against some of his most powerful foes. Washington says it wants to defeat Islamic State without helping Assad remain in power and hopes other anti-Assad groups can fill the vacuum.

But while U.S. planes have been striking Islamic State in eastern Syria, Assad's air force has been bombing other rebel groups in the west of the country, and his troops and allied Lebanese Shi'ite militia have advanced.

Syrian warplanes dropped projectiles including "barrel bombs" - oil drums filled with explosives - in Hama, Idlib, Homs and Aleppo provinces and around Damascus, the Observatory said.

Five people were killed when barrel bombs were dropped on al-Rastan city in Homs province and nine died in a barrel bomb attack east of the city of Aleppo, it said.

In Iraq, where the U.S. strikes have gone on for far longer and Washington is supporting government efforts to advance, Islamic State militants are changing tactics, ditching conspicuous convoys in favor of motorcycles and planting their black flags on civilian homes to confuse target spotters.

Witnesses and tribal sources in Islamic State-controlled areas report fewer militant checkpoints to weed out "apostates" and less cell phone use.Islamic State elements "abandoned one of their biggest headquarters in the village" when they heard the air strike campaign was likely to target their area, said a tribal sheikh from a village south of Kirkuk.

"They took all their furniture, vehicles and weapons. Then they planted roadside bombs and destroyed the headquarters," said the sheikh who declined to be identified. "They don't move in military convoys like before. Instead they use motorcycles, bicycles, and if necessary, they use camouflaged cars."

Tribal and local intelligence sources said an air strike on Thursday near Bashir town, 20 km (12 miles) south of Kirkuk, had killed two local senior Islamic State leaders while they were receiving a group of militants from Syria and Mosul. Ongoing fighting makes it impossible to verify the reports.

Sheikh Anwar al-Assy al-Obeidi, the head of a large tribe in Kirkuk and across Iraq, told Reuters there were now fewer killings because fighters could not operate as openly.

"They were executing people like drinking water ... Now the air strikes are very active and have decreased the (militants') ability," said Obeidi, who fled to Iraqi Kurdish-held territory this summer after Islamic State blew up his home.