BEIRUT – Islamic State has taken control of 90 percent of a Palestinian refugee camp on the Damascus outskirts where 18,000 civilians have suffered years of bombing, army siege and militia control, a monitoring group said on Saturday.

The hardline group’s offensive in Yarmouk gives it a major presence in the capital. Islamic State, the most powerful insurgent group in Syria, is now only a few kilometres from President Bashar Assad’s seat of power It also gives the group a potential sanctuary where US-led coalition forces were unlikely to strike because of the camp’s proximity to Damascus.

Palestinian officials and Syrian activists said the Islamic State was working with rivals from the al-Qaeda affiliate in Syria, the Nusra Front. The two groups have fought bloody battles against each other in other parts of Syria, but appear to be cooperating in the attack on Yarmouk.

The United Nations has said it is extremely concerned about the safety and protection of Syrians and Palestinians in the camp. Civilians trapped there have long suffered a government siege that has led to starvation and disease.

“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 said.