The UN Security Council on Monday demanded all parties to the Syrian civil war allow humanitarian aid to reach without obstruction the Yarmouk Palestinian refugee camp on the outskirts of Damascus, recently seized by Islamist militants.

The unanimous appeal by the 15-nation council came after Pierre Krahenbuhl, head of the UN agency for Palestinian refugees, UNRWA, told the council behind closed doors about "extreme circumstances and hardship" in the camp, a diplomat who attended the meeting said.

"Members of the Security Council called for unhindered humanitarian access to the Yarmouk Camp and for the protection of civilians," the statement said.

The council "stressed the need to support the emergency relief effort for civilians in Yarmouk including through funding the $30 million emergency appeal".

The camp, set up in 1957 to house Palestinians, has become a symbol of the desperate plight of people in rebel-held territory since the Syrian government laid siege to it in 2013.

Fighters from the hard-line Islamic State attacked the camp earlier this month, leading to a round of clashes with other militants. Most Islamic State fighters had withdrawn last week after largely defeating their rival, Aknaf al Maqdis, leaving the al Qaeda-affiliated Nusra as the main group in the camp.

The council condemned "all acts of terrorism perpetrated" and demanded that Nusra and Islamic State withdraw completely.

Before Islamist fighters arrived in Yarmouk, Western diplomats and UN officials say, it was armed forces supporting Syrian President Bashar al-Assad who were preventing camp residents from getting aid.

"It is critical that all parties, especially the Syrian government, support the U.N. framework for responding to the situation in Yarmouk," a US official said on condition of anonymity.

"The unremitting violence and the Assad regime's nearly two-year-old siege of Yarmouk have reduced the camp to a living hell for the thousands of residents still living there," the official added.

The council said it supported a three-point UN plan to assist civilians who were unwilling or unable to leave Yarmouk, help those who want to temporarily relocate from the camp to do so safely and aid Yarmouk residents who have already fled.

The camp was home to some 160,000 Palestinians before the Syrian conflict began in 2011, refugees from the 1948 war of Israel's founding and their descendants. The Syrian government says only 6,000 remain.