Khieu Samphan, a former head of state of the regime admitted it took place under the Maoist group's rule, but denied any personal responsibility for the deaths of up to two million people during the period.

ABC Radio Australia said the admission marks the first time a senior Khmer Rouge leader has conceded that genocide took place during its government in Cambodia from 1975 until 1979.

After watching a documentary film by French-Cambodian Rithy Panh, titled "S-21: The Khmer Rouge Killing Machine," Samphan said the film revealed enough for him to concede that genocide occurred.

Samphan is a prime candidate for prosecution once an international court is established to try the remaining Khmer Rouge leaders.

The United Nations and Cambodia agreed in June to establish an international tribunal to try surviving leaders.