Al-Qaeda-linked fighters fought rival Syrian rebels near the border with Turkey Wednesday, activists said, in an outbreak of violence driven by the divisions between factions battling President Bashar Assad.
The fighting illustrates the volatile situation in Syria as a team of chemical weapons experts start the process of eliminating the country’s chemical weapons stockpile, with inspections expected to begin next week.
The Al-Qaeda-linked Islamic State of Iraq and greater Syria (ISIS)  took control of the northern border town of Azaz last month, kicking out rival rebels and prompting Turkey to shut the crossing about 5 km away.
ISIS, which wants to merge Syria into a larger state ruled by Islamic law, has maintained control of the town since then and clashes have periodically erupted between it and fighters of the Northern Storm brigade, which they had expelled to its outskirts.
Activists said the latest fighting broke out Tuesday night after a deadline ISIS had set for Northern Storm fighters to surrender their weapons came to an end. 
“There are very fierce clashes on the outskirts of Azaz. ISIS cut all roads leading to Turkey and the situation is very tense,” said one rebel source, speaking from Turkey.
Another activist from Azaz said ISIS had seized two checkpoints and a base from Northern Storm and had advanced toward the border. He said some ISIS fighters had been killed, but he did not know how many.
The Syrian rebels have been undermined by infighting, partially over conflicting ideology, but more often over territory, spoils of war and control of resources and smuggling.
An activist in Azaz, Jamal Yusuf, said the border closure had made it harder for people to flee. The crossing was a lifeline for rebel-held northern areas, allowing refugees out and supplies in.
“People don’t want either of them. They don’t want ISIS and they don’t want Northern Storm. We’re saying to them, ‘Please leave us,’” he said.
ISIS includes a larger number of foreign fighters than other hard-line Islamist brigades fighting in Syria  and is viewed with suspicion by some other, less ideologically rigid rebel groups.
In an audio message this week, ISIS said its image was being distorted by a “widespread media campaign” against it that was trying to stir strife by blaming it for conflicts and ignoring its military victories or giving other groups credit.
The message accused the Northern Storm brigade of “opening a front” against them in the Azaz area and of conspiring with “the American pig, John McCain” to fight against Islamists.
U.S. Senator McCain, who has called for American military aid to rebels, visited Azaz in May and was photographed alongside Northern Storm fighters.
On the northern edge of Damascus, fierce clashes between Syrian troops and Al-Qaeda-linked fighters  killed at least 19 soldiers and pro-government militiamen in the past three days, according to the Britain-based Syrian Observatory for Human Rights.The fighting in the contested district of Barzeh flared Monday when the army stepped up attacks against opposition forces who have been trying to capture the area for months, the Observatory said. Districts such as Barzeh, on the edge of Damascus, are important for rebels based in the capital’s outer suburbs as the fighters try to move closer to the heart of the city.The rebels, mostly from Al-Qaeda-linked Nusra, sustained undisclosed losses, the Observatory said. It also noted clashes in Jobar on the capital’s eastern edge.
Fighting also continued in provinces across Syria, with clashes, shelling and airstrikes reported in the southern province of Deraa, the central Hama and Homs regions, and Aleppo and Idlib in the north.