DAMASCUS (AFP) -- The head of the UN agency for Palestinian refugees is to start an "urgent mission" to Syria on Saturday to discuss aid to civilians in Yarmouk refugee camp, amid reports that the Syrian regime has entered a new phase of fighting against the Islamic State group in the camp.
Pierre Krahenbuhl, who heads the UN agency for Palestinian refugees UNRWA, is to discuss the situation in the Palestinian camp on the outskirts of the Syrian capital and meet with displaced refugees.
The visit is "prompted by UNRWA's deepening concerns for the safety and protection of some 18,000 Palestinian and Syrian civilians, including 3,500 children" remaining in the Yarmouk camp, the agency said in a statement.
"Yarmouk remains under the control of armed groups, and civilian lives continue to be threatened by the effects of the armed conflict in the area," it said.
Krahenbuhl, who will meet displaced refugees on Sunday in a school near the camp, will discuss "with the government of Syria... peaceful approaches to addressing the humanitarian consequences of the situation in Yarmouk."
He will also meet with deputy special envoy Ramzy Ezzeldin Ramzy, who was sent by UN chief Ban Ki-moon on Friday to Damascus. Syria opens battle to defend Damascus
A new phase of fighting began inside the refugee camp on Saturday when the Syrian regime officially engaged IS in a battle to defend Damascus against the militant group.
Yarmouk, which is Syria's largest refugee camp lying seven kilometers south of Damascus, was initially attacked by IS on April 1, and the group subsequently took over up to 90 percent of the camp.
Armed Palestinian factions have fought back and Syria's air force has struck IS positions in the camp.
On Saturday, local reporters said that 13 Palestinian fighters were killed as fighting ensued between the Syrian regime and IS.
Their deaths add to a growing toll of Palestinian civilians and fighters since the camp's near take over by IS.
On Thursday, PLO envoy to Syria Ahmed Majdalani announced support from Palestinian factions in Syria for a joint military operation with the Syrian regime against IS.
However, the PLO later rejected involvement in a military campaign, citing their longstanding policy of non-interference in the internal affairs of Arab nations.
By Saturday, Majdalani said the situation was now out of the hands of the Palestinian leadership.
Majdalani told Ma'an that the resort to military action had been imposed on Palestinian groups by IS, and that negotiations would not be workable.
His comments mirrored those made by senior Fatah official Major-General Tawfiq al-Tirawi, who on Friday called on party members in Lebanon and Syria to arm themselves and head to Yarmouk to fight IS.
Al-Tirawi told Ma'an that although Palestinian refugees are neutral in Syria's civil war, "terrorist groups like IS, al-Nusra Front and others" had pushed Palestinians into the conflict.'The deepest circle of hell'
Although hundreds of residents have been evacuated, up to 18,000 residents remain inside the camp, which has been besieged by the Syrian army for more than a year.
The camp was once home to 160,000 people, Syrians as well as Palestinians, but its population has dwindled since the uprising erupted in March 2011.
On Thursday, UN chief Ban Ki-moon called for action to prevent a massacre at Yarmouk, warning: "A refugee camp is beginning to resemble a death camp."
Ban added: "In the horror that is Syria, the Yarmouk refugee camp is the deepest circle of hell."
More than 230,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests which spiraled into war after a regime crackdown.Ma'an staff contributed to this report.