Fighters allied to Al-Qaeda tightened their grip on a Syrian border town Thursday, as President Bashar al-Assad claimed most of the rebels fighting his forces were linked to the extremist group.

Elsewhere in the country, a bomb attack on a bus in the central province of Homs killed 14 civilians, an NGO said in an updated toll, adding to the more than 110,000 casualties of the 30-month conflict.

Residents said members of Al-Qaeda front group Islamic State of Iraq and the Levant (ISIS) overran the border town of Azaz on Wednesday after an hours-long firefight with Free Syrian Army (FSA) rebels.

Residents reached by Skype said ISIS men controlled all the checkpoints in the town and that FSA fighters appeared to have left.

Meanwhile, the Syrian Observatory for Human Rights reported that rebel fighters from Liwa al-Tawhid, one of Aleppo province's most powerful groups and allied to the FSA, had arrived in the area.

A spokesman for Liwa al-Tawhid told AFP via Skype the group "will work to try and calm the situation... We are doing our best to solve the differences and to find a solution that satisfies everyone".

Azaz, on the Turkish border, was one of the first towns to be overrun, in July 2012, by FSA rebels, who set up their own administration.

Tensions between some opposition groups and ISIS have spiralled in recent months, especially in northern Syria, where the opposition controls vast swathes of territory.

Several local groups resent ISIS's growing territorial control, its steady supply of arms, as well as its brutality, which opponents often compare to that of the regime's.

ISIS, on the other hand, has accused some rebels affiliated with the FSA's Supreme Military Command of collaborating with the West and of being "heretics".

Assad, in a confident interview Wednesday with US television network Fox News, insisted Syria was not gripped by civil war but was the victim of infiltration by foreign-backed Al-Qaeda fighters.

"What we have is not civil war. What we have is war. It's a new kind of war," he said, alleging that Islamist guerrillas from more than 80 countries had joined the fight.

"We know that we have tens of thousands of jihadists... we are on the ground, we live in this country," he said, after an expert report suggested that between 40 and 45 percent out of around 100,000 rebels were jihadists or hardline Islamists.

The president's latest television appearance came as UN envoys debated a draft resolution that would enshrine a joint US-Russian plan to secure and neutralise his banned chemical weapons.

Assad insisted in the interview that his forces had not been behind an August 21 gas attack on the Damascus suburbs that killed hundreds of civilians, but vowed nevertheless to hand over his deadly arsenal.

'About a billion'

"I think it's a very complicated operation, technically. And it needs a lot of money, about a billion," he told Fox.

"So it depends, you have to ask the experts what they mean by quickly. It has a certain schedule. It needs a year, or maybe a little bit more."

After last month's barrage of sarin-loaded rockets, which the West says was clearly launched by the regime, US President Barack Obama called for US-led punitive military strikes.

But with US lawmakers and the Western public not sold on the virtues of another Middle East military adventure, Assad's ally Russia seized the opportunity to propose a diplomatic solution.

Pressed by President Vladimir Putin, the White House agreed to hold fire while Russia and the international community -- with Assad's agreement -- draws up a disarmament plan.

That plan will face its first big test on Saturday, the one-week deadline announced by Moscow and the United States for Assad to provide a list of his chemical facilities.

Putin said Thursday he was confident but not 100 percent sure that Syria would carry out its commitments.

"Will we manage to carry it through? I can't say 100 percent, but all that we have seen recently, in the last few days, inspires confidence that it is possible and that it will be done," Putin told politicians and journalists at a meeting in the Novgorod region.

Meanwhile, US Secretary of State John Kerry urged China to play a "positive, constructive" role at the United Nations on the planned resolution.

He acknowledged at the start of talks with Chinese Foreign Minister Wang Yi that the two sides have "disagreed sharply" over the Syrian conflict.

But Wang said he was ready for "in-depth" talks on all issues, including Syria, "with an open mind."

Roadside bombs targeting a convoy of minibuses in the central province of Homs killed 14 civilians on Thursday, the Observatory said.

The blasts occurred on the road linking Homs city to a string of villages populated by Alawites, an offshoot of Shiite Islam to which Assad belongs.

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