Ban Ki-Moon described the Palestinian refugee camp to the south of the capital Damascus as "the deepest circle of hell" in Syria's four-year-long civil war.

"What is unfolding in Yarmouk is unacceptable," the UN secretary-general told reporters at UN headquarters in New York. "We simply cannot stand by and watch a massacre unfold."

On April 1, Sunni militant group IS took control of large parts of a Palestinian refugee camp in Yarmouk after fighting with Palestinian groups who also oppose President Bashar al-Assad's regime.

Yarmouk, which was previously a thriving neighborhood and home to 160,000 Palestinian refugees and Syrians, has been caught up in the country's fighting between government forces and Syrian insurgent groups, including al Qaeda's Nusra Front, for more than a year. Only about 18,000 residents are estimated to remain in the camp after many fled the fighting.

"The refugee camp is beginning to resemble a death camp," Ban warned, adding that Islamist militants were using refugees, including some 3,500 children, as human shields.

Ban demanded an end to the fighting, access to humanitarian aid, and safe passages for refugees who wish to leave the camp.

More than 2,000 refugees have fled the camp in the last few days.

'Unified opposition' against IS

On Tuesday, the Syrian government said it was ready to offer Yarmouk refugees weapons to aid their fight against IS.

Fierce clashes in Yarmouk have stopped, but government forces continue to bomb the area.

Syria's deputy foreign minister, Faisal Meqdad, meanwhile said his government "had used all its efforts to present humanitarian and medical aid to Palestinian refugees" and helped them to exit the area.

Anwar Abdul Hadi, an official of the Palestine Liberation Organization (PLO) told journalists: "Syrian authorities are ready to support the Palestinian fighters in a number of ways, including militarily, to push IS out of the camp."

Palestinian officials under the leadership of PLO's Ahmad Majdalani said that they had agreed with Damascus on a "unified position for Palestinian forces in Syria in coordination with the Syrian government." If finalized, the deal would represent a breakthrough, since most Palestinian refugees in the camp were against Syrian President Bashar al Assad's regime.

shs/kms (AFP, AP)