In a statement read on television, Hun Sen said he supported the punishment of Khmer Rouge crimes, but it was up to the courts to decide who should face trial.

Pol Pot: Khmer Rouge "Brother number one" died in April

He said: "My stance is this: the trial of the Khmer Rouge is over, but the issue still continues to exist. It is over based on the verdict of the people's court in 1979, which is still valid and acknowledged by the royal decree granting amnesty to Ieng Sary in 1996.

"The issue that still exists is that of the establishment of a tribunal based on the views of international and national jurists who are now doing their work."

He also denied agreeing to give the two Khmer Rouge leaders - Khieu Samphan and Nuon Chea - an amnesty as part of the deal made when they defected last Friday.

The prime minister said he was hurt by the criticism of his comments at the time suggesting a trial would not be in the national interest.

An aide of the two Khmer Rouge leaders had earlier warned that any trial for genocide would expose the role of foreign powers in Cambodia. The aide, Long Norin, mentioned specifically the United States and China.

Around 1.7m people are believed to have died under the Khmer Rouge regime

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 two men surrendered to the Cambodian Government late last week after striking a deal with Hun Sen, who said at the time that it would not be in the national interest to hold a trial.

Possible international trial

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 on the feasibility of a trial.

There has been controversy over the warm welcome given to the two Khmer Rouge leaders by the authorities. They have begun a seaside holiday break and had lunch at the prime minister's residence.

Khieu Samphan, former nominal leader of the Khmer Rouge, and Nuon Chea, the movement's chief ideologue, were key figures in Cambodia's reign of terror.

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