Syrian activists and a Lebanon-based TV station are reporting that Islamic State militants have infiltrated a Palestinian refugee camp in the Syrian capital, Damascus, and are fighting with a group inside the camp.

The reports mark the deepest infiltration yet by ISIS militants into Damascus. If they gain control of the Yarmouk camp, they can threaten President Bashar Assad's seat of power.

The Britain-based Syrian Observatory for Human Rights says clashes broke out Wednesday in Yarmouk between ISIS fighters and members of the Palestinian faction called Aknaf Beit al-Maqdis.

The Beirut-based Al-Mayadeen TV says the ISIS extremist fighters entered the camp from the nearby neighborhood of Hajar Aswad. That southern Damascus neighborhood is controlled by militants.

Observatory's chief, Rami Abdurrahman, says ISIS "now controls large parts of the camp."