The last surviving senior Khmer Rouge leader denied responsibility for genocide committed more than 40 years in Cambodia during his closing remarks Thursday to an international tribunal.

The last surviving senior Khmer Rouge leader denied responsibility for genocide committed more than 40 years ago in Cambodia during his closing remarks Thursday to an international tribunal.

Under the ultra-Maoist Khmer Rouge regime led by "Brother Number 1" Pol Pot, some two million Cambodians died from overwork, starvation and mass executions from 1975 to 1979.

Khieu Samphan -- one of the secretive regime's few public faces -- was sentenced in 2018 by a UN-backed court to life in prison for genocide committed against ethnic-minority Vietnamese.

But his lawyers have argued since Monday in daylong appeal hearings that the tribunal took a "selective approach" to witness testimony to convict him.

"I categorically refuse the accusation that I had the intention to commit the crimes," the 90-year-old said Thursday at the end of the hearings.

"I have never committed them."

The three-year trial, which ended in 2017, included the testimony of more than 100 witnesses who described in chilling detail the abuses and mass murders committed against Cham Muslims and ethnic Vietnamese.

Khieu Samphan claimed he was not part of the killing machine that exterminated nearly a quarter of Cambodia's population, rejecting in forceful closing statements the label of "murderer".

But the court sentenced him to life in prison -- alongside "Brother Number 2" Nuon Chea who died in 2019 -- for genocide and a litany of other crimes, including forced marriages and rapes.

The pair were previously handed life sentences by the 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 rural labour camps.

Whatever the verdict to his appeal on genocide charges may be, Khieu Samphan said Thursday his fate was already sealed.

"No matter what you decide, I will die in prison," he said. "I'm judged symbolically, rather than by my actual deeds as an individual."

The verdict for the appeal is expected to come in 2022.