The U.N. Security Council called Monday for life-saving assistance and safe evacuation for up to 18,000 Palestinians facing escalating fighting in a refugee camp in the Syrian capital and what the U.N. official in charge described as "a completely catastrophic" humanitarian situation.

The council, after an emergency meeting, condemned "the grave crimes" committed by the Islamic State extremist group and al-Qaida-linked al-Nusra against civilians in the Yarmouk camp and said their crimes must not go unpunished.

It called for protection of the refugees, humanitarian access to the camp, and safe passage and evacuation of the civilians — and said it will look into further measures to help achieve this.

Pierre Krahenbuhl, head of the U.N. agency for Palestinian refugees known as UNRWA, told reporters after briefing the council that the situation in Yarmouk "is more desperate than ever" as the result of the sudden upsurge in fighting by probably half a dozen opposition groups and some groups supporting the Syrian government.

The UNRWA chief said "a significant percentage of civilians" are now in areas of the camp controlled by armed groups including the Islamic State group. He said he had heard reports of beheadings in Yarmouk but was unable to verify them.

Krahenbuhl urged political and religious leaders with influence on the combatants to pressure them to observe international human rights and humanitarian law which requires protection of civilians. He said the refugees are very weak — existing on about 400 calories a day compared to a normal intake of about 2,100 calories — and their only concern now is "basic and bare survival."

The situation in Yarmouk is currently too dangerous for any aid to be delivered and he appealed for a humanitarian pause to get food and medicine into the camp and get those who want to leave out safely.

Earlier, the Palestinian U.N. Ambassador Riyad Mansour urged the council to take action to ensure safe passage the refugees besieged at Yarmouk. He appealed to all nations to help the refugees relocate to safer areas in Syriaor in other countries.

Mansour said about 2,000 of the estimated 18,000 refugees in Yarmouk had made it to safety on their own.

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He said that saving the Palestinian refugees in Yarmouk is his government's top priority, adding that Palestinian President Mahmoud Abbas was in Jordan, which currently holds the Security Council presidency, discussing the best ways to help them.

Krahenbuhl, who spoke to the council and reporters by videoconference from the Jordanian capital Amman, said there are about 470,000 Palestinian refugees still in Syria, and over half are displaced.