The aide, Long Norin, said a trial of the two defecting Khmer Rouge leaders would expose the role of foreign powers in Cambodia - specifically the United States and China.

"A lot of people are involved and it's very complicated. If they push for this, we will dig up the past and present our own case," he said.

A hotel on the Sihanoukville beach - VIP treatment

There have been growing calls for the two men - Khieu Samphan and Nuon Chea - to be tried on genocide charges for their actions in the Khmer Rouge government, which is held responsible for the deaths of an estimated 1.7 million people.

The leaders surrendered to the Cambodian Government late last week after striking a deal with Prime Minister Hun Sen.

There has been controversy over the warm welcome given to the two men by the authorities. They have been on a trip to the seaside and had lunch at the prime minister's residence.

Hun Sen has said it would not be in the national interest to hold a trial. Correspondents say he may be under pressure from states like China and Thailand to avoid a hearing.

However, on Friday he attacked Thailand for hosting the leaders and forcing him to accept defections rather than having them stand trial, French news agency AFP reported.

King Norodom Sihanouk and his son, the ousted prime minister Prince Norodom Ranariddh, have said they support the idea of an international trial. Several members of the king's family were killed by the Khmer Rouge.

The US, Britain and France have all issued strong statements saying that leaders of the Khmer Rouge must be held accountable for their action.

Experts hired by the United Nations are looking at the possibility of an international tribunal, along the lines of those for Rwanda and Bosnia.

They are due to report next month, but BBC Cambodia Correspondent Caroline Gluck says without the full co-operation of the Cambodian Government it will be hard to see how that might happen.