An aide to two defecting leaders of the Khmer Rouge has warned that any move to try them for genocide would expose the roles of foreign powers in Cambodia.

The aide Long Norin mentioned specifically the United States and China.

There have been growing calls for the two men, Khieu Samphan and Nuon Chea, to stand trial for their actions as part of the Khmer Rouge government which ran Cambodia in the 1970s.

The two men defected late last week after striking a deal with the prime minister, Hun Sen, who has said it would not be in the national interest to hold a trial over the deaths of an estimated one-point-seven million people during the Khmer Rouge's rule.

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