There's growing criticism in Cambodia of the government's decision to allow two former Khmer Rouge leaders, who surrendered over a week ago, to return to the former Khmer Rouge stronghold of Pailin.

A leading human rights campaigner, Lao Mong Hay, said the government should have detained the men, Khieu Samphan and Nuon Chea, pending a United Nations' decision on whether to try them for crimes against humanity.

Mr Lao warned it would be extremely hard for the government to arrest them in Pailin.

A coalition of human rights groups is trying to gather half-a million signatures to petition Phnom Penh to support and initiate efforts to bring the two leaders to justice.

Since defecting, Khieu Samphan and Nuon Chea have been given privileged treatment by the government.