The Phnom Penh Post, which reported his death, had said a day earlier Ieng Sary, one of the leaders widely identified with the inhuman Khmer Rouge regime of the 1970s, had been in critical condition.
Kyodo News Agency quoted Ieng Sary's son Ieng Vuth as saying his father died of illness and old age.
Ieng Sary was the oldest of the three members of the Khmer Rouge regime facing trial before a U.N.-backed panel on war crimes, genocide and crimes against humanity charges, stemming from the deaths of hundreds of thousands of Cambodians when Khmer Rouge ruled the country between 1975 and 1979. Some estimates say up to 2 million people died from political executions, starvation and forced labor.
The U.N.-baked tribunal was set up as part of a joint agreement between the Cambodian government and the United Nations to try leaders of the Khmer Rouge for war crimes and crimes against humanity.
Ieng Sary, along with the other accused Nuon Chea and Khieu Samphan, had denied the charges against them. Pol Pot, another of the notorious Khmer Rouge leaders, died in 1998. The tribunal earlier had found Ieng Thrith, Ieng Sary's wife who had been a minister in the Khmer Rouge regime, unfit to stand trial because of her medical condition.