The last surviving senior Khmer Rouge leader will next week begin an appeal against his life imprisonment for his role in the genocide committed by the regime in Cambodia more than four decades ago.

The Khmer Rouge, led by "Brother Number 1" Pol Pot, left some two million Cambodians dead from overwork, starvation and mass executions from 1975-79.

The regime's former head of state Khieu Samphan, 90, will on Monday challenge his 2018 conviction for genocide against ethnic minority Vietnamese.

He was convicted alongside "Brother Number 2" Nuon Chea and jailed for life for genocide and a litany of other crimes, including forced marriages and rapes.

The pair were previously handed life sentences by the UN-backed court in 2014 for crimes against humanity over the violent forced evacuation of Phnom Penh in April 1975, when Khmer Rouge troops drove the population of the capital into the countryside.

Nuon Chea died in 2019, leaving Khieu Samphan the sole surviving Khmer Rouge leader to challenge the landmark ruling.

Khieu Samphan's defence team has asked the Extraordinary Chambers in the Courts of Cambodia (ECCC) to overturn the judgment.

"We will ask the court to acquit Khieu Samphan of the genocide," his lawyer Kong Sam Onn told AFP Thursday.

Former Khmer Rouge head of stage Khieu Samphan will appeal against his 2018 life sentence for his role in the regime's genocide in Cambodia in the 1970s
Former Khmer Rouge head of stage Khieu Samphan will appeal against his 2018 life sentence for his role in the regime's genocide in Cambodia in the 1970s Extraordinary Chambers in the Courts of Cambodia / NHET SOK HENG

Tribunal spokesman Neth Pheaktra said the hearing would take place from Monday to Thursday and due to Covid-19 curbs, Khieu Samphan and his defence team will sit in a separate room from the judges who will be in the main courtroom.

Khieu Samphan is expected to testify, he added.

Pol Pot, who wanted to transform Buddhist-majority Cambodia into an agrarian utopia, died in 1998 without facing trial.

Former Khmer Rouge foreign minister Ieng Sary and his wife also died before they could be tried.

The hybrid court, which uses a mix of Cambodian and international law, was created with UN backing in 2006 to try senior Khmer Rouge leaders.

It has convicted only three people so far and cost more than $300 million.

Strongman Prime Minister Hun Sen -- himself a former Khmer Rouge cadre -- has spoken against any further cases, claiming it would plunge the country into instability.

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