Pen Sovann was the country's first post-Khmer Rouge prime minister, holding the office from June to December 1981, when it was known as the People's Republic of Kampuchea. He died Saturday night from an illness in his hometown in southern Takeo province.

In late 1981, Pen Sovann was removed from power by the Vietnamese in an ouster triggered by his calls for the withdrawal of Vietnam's forces from Cambodia. He was imprisoned for 10 years in Hanoi.

Pen Sovann founded the Cambodian National Sustaining Party, which took part in the 1998 election but did not win a seat in parliament. In 2012, he joined the opposition Cambodia National Rescue Party and won a parliamentary seat in the last general election in 2013.

Pen Sovann was part of a group of self-exiled former Cambodian communists who fled Cambodia after becoming disenchanted with the Khmer Rouge. He later returned amid the Vietnamese military invasion that toppled the Khmer Rouge.

He was also the bitter rival of current longtime Cambodian Prime Minister Hun Sen.

In a statement Sunday, the Cambodia National Rescue Party said it was joining Pen Sovann's family in organising a funeral for Pen Sovann.

The party's self-exiled leader, Sam Rainsy, said on his Facebook page Sunday that Sovann had dedicated his life to the Cambodian people.