This picture taken on Jan. 31, 2014, and released by the United Nations Relief and Works Agency for Palestine Refugees (UNRWA), shows residents of the besieged Palestinian camp of Yarmouk, queuing to receive food supplies, in Damascus. — AP BEIRUT — Syrian activists say militants linked to Daesh (the so-called IS) have taken over the majority of neighborhoods in a Palestinian refugee camp on the edge of Damascus as fighting continues for the fourth day. They say the militants include the Daesh group and the Nusra Front, the Al-Qaeda affiliate in Syria. The two groups are rivals in Syria but appear to be cooperating in the attack on the Yarmouk camp. An activist in southern Damascus, Hatem Al-Dimashqi, said Saturday that rebel groups have launched a counteroffensive aimed at ousting the militants from the camp. The Daesh militants stormed the Yarmouk camp on Wednesday, marking the extremist group's deepest foray yet into Damascus. Damascus-based Palestinian official Khaled Abdul-Majid said on Saturday that the Daesh group was holding almost half of the camp. 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. “Yarmouk is a test, a challenge for the international community. We must not fail. The credibility of the international system itself is at stake,” he said. The Daesh supporters posted photos on social media of the severed heads of two men they said had been beheaded after fighting for Aknaf Beit Al-Maqdis. Yarmouk was home to half a million Palestinians before the Syrian conflict began in 2011. The was has killed 220,000 people and displaced millions. The United States on Friday condemned the latest wave of violence in Syria which has left dozens of civilians dead and displaced thousands more. State Department spokeswoman Marie Harf said in a statement that the Daesh militants had massacred more than 40 people in Mabujeh in Hama province, including women and children, while regime forces also bombed the town. “The United States strongly condemns attacks this week against Syrian civilians,” Harf said. The US is also “deeply concerned” by attacks on the Yarmouk refugee camp in Damascus, Harf said, which had left 18,000 civilians in the area at risk. “Yarmouk's inhabitants have already suffered from the regime's violence and have lived under siege for nearly two years, deprived of desperately needed essentials, including food and medical relief,” Harf said. “The United States reiterates that all forces must cease unlawful attacks on civilians and comply with international law.” — Agencies