The U.N. human rights office in Cambodia said on Wednesday it was "gravely concerned" about scores of arrests, disappearances and torture-killings since the government began a crackdown on opposition protests last week.

Among the bodies found were those of three women and two people in the clothing of Buddhist monks, Thomas Hammarberg, the U.N.'s special representative for human rights in Cambodia, said in a statement."During the past week at least two people have been killed during the demonstrations, while the bodies of 16 others have been found floating in rivers, in irrigation ditches and in shallow graves around the capital," he said.

Hammarberg said his office was investigating a further dozen reports of bodies being found by villagers in the vicinity of Phnom Penh and numerous missing persons reports from relatives.

"Many of the bodies bear the signs of torture or other violence, including bullet wounds and strangulation marks," the statement said. "Several of the bodies had their hands tied behind their back and were gagged and blindfolded."