The man who was Cambodian head of state under the Khmer Rouge, Khieu Samphan, has admitted that the government at the time committed genocide.
Khieu Samphan said he knew nothing of the killings
It is the first time that a senior Khmer Rouge figure has conceded that mass killings took place while the party was in power between 1975 and 1979.
Khieu Samphan is likely to be among surviving party leaders to stand trial on genocide charges as soon as next April.
His comments, given to two Western news agencies, appeared designed to distance himself from responsibility for what happened..
"I have found it so difficult to believe what people told me of what happened under the Khmer Rouge regime, but today, I am very clear that there was genocide," Khieu Samphan told the AFP news agency.
But he also released an open letter saying that he had no knowledge at the time of the mass executions.
"I was not involved in any killings," he told the Associated Press.
In March this year, the Cambodian government and the United Nations finally agreed to set-up a joint Cambodian-international tribunal to try former Khmer Rouge leaders.
The agreement has yet to be ratified by the Cambodian parliament because of political deadlock following elections.
As the public face of the Khmer Rouge, Khieu Samphan is almost certain to be among those in the dock.
He is likely to be joined by former Khmer Rouge foreign minister Iang Sary, and Nuon Chea, who was known as "Brother Number Two".
The former military commander Ta Mok is already in prison awaiting trial, while Pol Pot, the Khmer Rouge leader, died in 1998.