Palestinian officials and activists say Islamic State militants are battling against armed groups inside a refugee camp in the Syrian capital, Damascus, and have made new advances inside the camp.

The militants stormed the Yarmouk camp on Wednesday, marking the extremist group's deepest foray yet into Damascus. They were expelled Thursday but officials said they re-entered the camp Friday.

One Palestinian official, Khaled Abdul-Majid, said the group is in control of half of the camp. The London-based Syrian Observatory for Human Rights also reported new advances by the group in the camp.

Abdul-Majid and another official, Anwar Raja, said the militants are fighting a Palestinian faction called Aknaf Beit al-Maqdis.