Islamic State clashed with rebel groups in a besieged Damascus neighborhood Wednesday, in a sign that the militant group might be trying to take control of the area.

Local activists said that fighters from the Sunni extremist group entered urban refugee camp Yarmoukafter some of its members were detained by Aknaf Bait al-Maqdis, an opposition group allied with Hamas and based in the camp, following the assassination of one of its leaders.

The Syrian Observatory for Human Rights reported that Islamic State had advanced into Yarmouk, which houses Palestinians on the outskirts of Damascus, and seized the south and southwestern sections of the neighborhood.

Unlike other parts of Syria where Islamic State controls territory with no tolerance for other factions, in southern Damascus, a broad spectrum of militant and rebel groups coexist, including al Qaeda’s Nusra Front, Free Syrian Army groups and the Salafist Ahrar Al Sham. Occasional fighting between the groups in southern Damascus’s numerous rebel-controlled neighborhoods isn’t uncommon.

One activist said Islamic State’s aim is to push other competing armed groups out of Yarmouk.