An assault by Syrian security forces on a Palestinian refugee camp in the coastal city of Latakia amounts to a crime against humanity, a senior official in the Palestine Liberation Organisation said.

"The shelling is taking place using gunships and tanks on houses built from tin, on people who have no place to run to or even a shelter to hide in," Yasser Abed Rabbo, the PLO secretary general, told Reuters. "This is a crime against humanity."

Residents of Latakia say Syrian security forces have been targeting areas where demonstrators have been protesting against President Bashar al-Assad's rule.

UNRWA, the U.N. agency that cares for Palestinian refugees, said its latest reports indicated that al-Raml camp, home to 10,000 registered refugees, was now almost completely deserted.

On Monday, UNRWA reported that four refugees had been killed and 17 wounded in the violence. "Our fear is that without access, the figures are higher, but we simply don't know," Chris Gunness, UNRWA spokesman in Jerusalem, said.

"It's obviously been the scene of a security or military operation. We remain extremely concerned. UNRWA needs to get in there. We need urgent humanitarian access," he said.

"Things get more and more grim and worrying by the minute. A forgotten population has now become a disappeared population," he said.