Syria's fighting has uprooted more than half of the country's 530,000 Palestinians — descendants of refugees from a Mideast conflict half a century ago — and their situation is becoming increasingly desperate, the head of a U.N. aid agency said Thursday.

The Palestinians in Syria are particularly vulnerable because of their refugee status, Filippo Grandi, head of the U.N. Relief and Works Agency, told The Associated Press in an interview.

He said most of the 12 Palestinian camps have been affected by the fighting.

"Armed groups and the government are confronting each other near the camps, inside the camps, and most or a large portion of the Palestinian population has had to leave those camps," he said after a two-day visit to Syria.

He estimated that 70 percent to 80 percent of the Palestinians have been affected by Syria's civil war. "Many of them, maybe more than half ... are displaced from their homes," he said.

He said about 54,000 have fled to Lebanon and several thousand to Jordan and Egypt, while others have sought shelter elsewhere in Syria. "These are refugees that became refugees a second time," he said. "It's really a very tragic situation."

Grandi's agency provides support for some 5 million Palestinians in Jordan, Syria, Lebanon, the West Bank and Gaza. They are descendants of hundreds of thousands of Palestinians who fled or were driven out of their homes during the fighting over Israel's 1948 creation.

When the Syria conflict erupted in March 2011, most Palestinians initially remained on the sidelines, though some joined protests against Syrian President Bashar Assad.

As a popular uprising escalated into an armed insurgency and then a civil war, some Palestinians joined the fight — some siding with the rebels and others with the regime.

The Yarmouk refugee camp, a sprawling neighborhood of 150,000 Palestinians on the outskirts of the capital Damascus, has been the scene of heavy clashes in recent months. Palestinian officials have said more than 700 camp residents have been killed in fighting, and that many of the others have left.

"The Yarmouk area is controlled by a variety of groups," Grandi said Thursday. "There are continued tensions and clashes with government forces, so it's a difficult situation for people to come back to."

He said he visited another Damascus area camp on Thursday and encountered many displaced Yarmouk residents there. "They are really in a very desperate situation because they even have no news about their houses, which may be destroyed, and their relatives (who) remained inside," he said.

Grandi appealed to the Syrian government and rebel fighters to allow the U.N. to deliver aid to the Palestinian camps. "We cannot do that and many people are at risk of their lives if we cannot resume the delivery of assistance," he said.

Overall, the Syria fighting has displaced several million people, including hundreds of thousands who fled to neighboring countries. More than 70,000 people have been killed, according to U.N. estimates.