The militants, reportedly entered the camp from the nearby Hajar Aswad neighborhood in southern Damascus in a coordinated attack with their rivals in the Al Qaeda-affiliated Nusra Front.
According to the UK-based Syrian Observatory for Human Rights, ISIS managed to take control of large parts of the Yarmouk camp following clashes with a Palestinian group.
The Observatory reported heavy clashes in the camp between ISIS fighters and members of the Palestinian faction called Aknaf Beit al-Maqdis.
Anwar Raja, the spokesman for the pro-Syria government Popular Front for the Liberation of Palestine said to mail online 'The Nusra Front opened the road for them in order to infiltrate the camp and several hours ago they entered Yarmouk”.
It was not immediately clear why Nusra - who have repeatedly fought against ISIS over the past year - would facilitate the entry of the group into the camp.
Residents of the camp queuing to receive food
A Syrian foreign ministry statement today said it holds Jordan responsible for 'obstructing the movement of trucks and passengers and any ensuing economic or social repercussions.'
Jordanian government spokesman Mohammed al-Momani said that the Nasib crossing was temporarily closed late last night because of clashes nearby.
A truce in the Yarmouk refugee camp allowed the UN to resume humanitarian activities but many still fear ISIS militant attacks, ABC reports
The United Nations has called for an immediate halt in the bloody attack by ISIS militants on a Palestinian refugee camp in neighborhood of Damascus.
Details are yet to emerge on the civilian toll but UN and Palestinian officials confirmed ISIS militants entered Yarmouk camp, sparking fierce clashes.
The UN Relief and Works Agency said there are a variety of groups engaged in serious fighting near the 18,000 refugees in the camp, including 3,500 children.
Christopher Gunness, spokesman for the UNRWA for Palestinian Refugees in the east, said the civilians are "at extreme risk of death, of serious injury, of trauma and of displacement".