The savage Islamic State (ISIS) organization has seized nearly all of the Palestinian district of Yarmouk in Damascus, activists said Saturday, and there are reports of beheadings and mass killings of Palestinians.

The London-based Syrian Observatory for Human Rights (SOHR) watchdog group said the Islamist militants have taken over 90% of Yarmouk, on the southern edge of the Syrian capital.

The Financial Times cited activists who said that the jihadi group may succeed in cementing a foothold in the Syrian capital, thus increasing pressure on President Bashar al-Assad.

ISIS supporters have reportedly posted pictures of fighters beheaded by the jihadi group during the battle.

“Reports of kidnappings, beheadings and mass killings are coming out from Al-Yarmouk,” said Saeb Erekat, an member of the Palestinian Liberation Organisation’s executive committee, Saturday evening. “The priority must be to save the Palestinian refugees in the camp by creating a safe passage for them out of the death trap that Al-Yarmouk has become.”

He called on the UN, the International Committee for the Red Crescent (ICRC) and the Syrian government to help evacuate civilians.

The main group fighting ISIS inside the camp is Aknaf Beit al-Makdis, an offshoot of Hamas. Two opposition sources told the Financial Times the Syrian army had allowed a Palestinian militia allied to Assad’s forces to send weapons to the Hamas offshoot fighting in Yarmouk.

“It’s an extremely rare thing for the government to do anything even remotely co-operating with the opposition,” said one activist. “That shows you how desperate the regime is to stop ISIS from having gateway right to heart of the capital for car bombs or whatever other atrocities.”

International Business Times explained that Yarmouk has been the scene of a fierce three-way fight since ISIS entered it last week

The Sunni ISIS group struck an alliance with rival jihadi group Jabhat al-Nusra, to wrest control Yarmouk from the rebels loyal to Hamas, which had been fighting against regime troops.

Jabhat al-Nusra and ISIS “were able to take control on 90% of the Yarmouk camp after violent clashes against Aktaf Bait al-Maqdis and Islamic battalions,” SOHR reported, adding that two men from the latter group were beheaded by ISIS.

“Five soldiers in regime forces were killed after clashes against Islamic battalions in the camp,” SOHR added, reporting also bombardments by regime forces in the area.

The UN expressed concern about the situation in the refugee camp which was once home to between 100,000 and 150,000 Palestinians and Syrians, and now holds only about 18,000.

“The situation in Yarmouk is an affront to the humanity of all of us, a source of universal shame,” UN Relief and Works Agency (UNRWA) spokesman Chris Gunness told Reuters.

“Yarmouk is a test, a challenge for the international community. We must not fail. The credibility of the international system itself is at stake”.