Former leaders of Cambodia's Khmer Rouge being tried by a U.N.-backed genocide tribunal have apologized directly to some of the families of victims of the regime's atrocities.

Khieu Samphan, the head of state of the 1970s communist regime, and Nuon Chea, its ideologist, were responding Thursday to questions from the so-called civil parties, who have an official role in the trial representing the victims' families.

Khieu Samphan said he was unaware at the time of the atrocities of the Khmer Rouge — whose radical policies led to the deaths of an estimated 1.7 million Cambodians — and held no real power in the regime, a claim disputed by scholars.

He and Nuon Chea apologized for the atrocities but said they acted in what they believed were the country's best interests.