At least 18 Palestinians were killed Thursday and their bodies displayed publicly in Damascus, PLO officials in the capital’s largest refugee camp said.
The PLO office in Yarmouk said the Syrian regime "committed a massacre" against Palestinians in the camp. Bodies were found mutilated and charred, it said.
PLO secretary-general Yasser Abed Rabbo denounced the killings.
"We reject any justification or allegations invoked by the Syrian regime army about this massacre which includes torture, killing, and assassination,"Abed Rabbo said.
"Moreover, such types of crimes need to be condemned internationally. Syria faces unprecedented massacres against Syrian people as well as Palestinians," he said.
Thursday’s killings were the latest in a string of attacks targeting Palestinians. At least 10 refugees were killed in the Yarmouk a day earlier, activists in the camp reported.
An activist in Yarmouk, where rebels have been hiding out in recent days, said tanks and soldiers had sealed all the entrances. Hundreds of soldiers were searching the area on foot and on trucks mounted with heavy machine guns.
"We are trapped here. Only children and older men or women can leave. Young men, who could be rebels or activists, and even young women, who could also be activists, are stuck inside," an activist called Abu Salam told Reuters on Skype.
"We are hiding in our homes. I am afraid to leave the house so I am sitting here waiting to see if they reach my street, if I will be arrested or shot dead," he said.
He said at least three people, two men and a young women, were shot dead when soldiers saw them running out of a park on Thursday morning. Another five rebels found hiding out in the area were executed, he said.
The campaign is the latest step in an effort by state forces to stamp out a presence in the Syrian capital of insurgents who are fighting to topple President Bashar Assad.
A resident who toured Yarmouk a day earlier said rebel fighters, who have been flushed out of many surrounding districts, had pulled into a southern section of the district and come under intense army bombardment overnight.
Activists and witnesses who spoke to Reuters say that many parts of the districts in Damascus’s southern outskirts, where insurgents have been trying to maintain a foothold, have been reduced to rubble.
They said entire buildings had collapsed and the stench of decaying bodies filled the streets. "We are too afraid to go get them because security forces are there and will ask why we are coming for these people," said Abu Salam.
Yarmouk is an unofficial camp for Palestinian refugees. The densely populated, impoverished district in southern Damascus is packed with concrete buildings.
This summer, many districts of southern Damascus became a daily battleground in an 18-month-old popular revolt against Bashar Assad that has escalated into civil war.
Syrian state television said 100 people had been arrested in Yarmouk, and said its forces searching another nearby district were "raiding terrorists dens" and had killed several people inside them.
Assad’s supporters say they are not facing homegrown opposition but rather militants funded from abroad.