Somewhere in Damascus, Bashar al-Assad was surely smiling at the news out of northern Syria this week.
Rebel groups loosely united in the cause of toppling Mr. al-Assad's regime openly battled each other in the north and northeast of the country, as Syria's savage civil war – which has already killed more than 100,000 people – continued its devolution into a three-sided, or even four-sided, fight.
The force turning the conflict on its head is the al-Qaeda-affiliated Islamic State of Iraq and the Levant (ISIL). The fierce, well-funded jihadi movement – with fighters hardened by wars in Iraq, Afghanistan and Chechnya – has been gaining strength and territory in recent months, while establishing strict Islamist rule over the areas it controls.
ISIL seized the town of Azaz, near the border with Turkey, on Wednesday, driving out fighters affiliated with the mainstream Free Syrian Army (FSA), which had held Azaz for more than a year. That provoked fierce battles that left at least five FSA fighters dead.
A truce was declared on Friday, but residents of southern Turkey reported hearing gunfire coming from Azaz hours after it was supposed to have taken effect. The Syrian National Coalition, an umbrella group claiming to represent the bulk of the anti-Assad movement, issued a statement condemning ISIL "for its aggression toward Syrian revolutionary forces and its indifference to the lives of the Syrian people."
"The Islamists certainly have more momentum, because of the speed with which they emerged, and the funding – which they must be getting from the [Arab states of the Persian] Gulf – and the ferocity and the large number of foreign fighters," said Paul Salem, director of the Carnegie Middle East Centre in Beirut.
The infighting – and the growing strength of the jihadis – feeds two opposing arguments: the FSA's plea for more aid from the West, and Russian President Vladimir Putin's argument that the fall of Mr. al-Assad would be a victory for extremists. "The key question is: Will anybody stand up and support the FSA seriously?" Mr. Salem said.
The growing sway of the Islamists also complicates the question of who would represent the anti-Assad rebels at any peace conference. In the northeast of the country, Kurdish militias that drove the Assad regime out months ago, also now find themselves battling ISIL and the allied al-Nusra Front, another jihadi group.
"You're beginning to see a division [of Syria] into three political spheres. A Kurdish northeast, a Sunni-dominated middle and north, and an Alawite minority-dominated coast and south," said Joshua Landis, a Syria expert at the University of Oklahoma. Mr. al-Assad's family and power base are Alawites, a sect of Shia Islam.
The ISIL offensive appears aimed at seizing strategic assets – such as grain-distribution centres and power stations – that would allow the organization to provide basic services in the areas it controls, services that can buy the loyalty of the local population.
"They're smart – much smarter than the FSA," Prof. Landis said. "They understand that providing energy and providing food are the basic elements of a future state."
The fracturing of the rebel movement – foreshadowing the possible disintegration of the country – comes as the United Nations Security Council prepares to debate a resolution that will outline the steps and time-table for the removal of the Syrian government's store of chemical weapons.
Facing the threat of punitive U.S. airstrikes following an Aug. 21 sarin-gas attack that killed hundreds in rebel-held areas on the outskirts of Damascus, Mr. al-Assad – who denies his forces were behind the gas attack – agreed to a Russian proposal that will see his chemical weapons handed over for destruction.
The United States, Britain and France are pushing to have the Security Council resolution include the possibility of military action if Mr. al-Assad does not comply. However, Russia has promised to veto any resolution that threatens force.
Syria began submitting information outlining the scope of its chemical-weapons program on Friday to the Netherlands-based Organization for the Prohibition of Chemical Weapons (OPCW). The regime is believed to possess about 1,000 tonnes of mustard gas, VX and sarin.
"We have received part of the verification and we expect more," a spokeswoman for the OPCW said.