Two senior leaders of the Khmer Rouge were sentenced to life in prison on war crimes charges for their role in Cambodia's terror period in the 1970s.

A UN-backed war crimes tribunal yesterday announced the historic verdicts, three and a half decades after the genocidal rule of the Khmer Rouge ended. The sentences are for Khieu Samphan, the regime's 83-year-old former head of state, and Nuon Chea, its 88-year-old chief ideologue, the only two leaders of the regime left to stand trial.

The tribunal's chief judge Nil Nonn asked both men to rise for the verdicts but the frail Nuon Chea said he was too weak to stand from his wheelchair and was allowed to remain seated.

There was no visible ­reaction from either of the accused as the judge said both men were found guilty of crimes against humanity, forced transfers, forced disappearances and attacks against human dignity and sentenced to life imprisonment.

The men can appeal against the rulings, but Nil Nonn told the court that "given the gravity of the crimes" both would remain in detention. The case, covering the forced exodus of millions of people from Cambodia's towns and cities and a mass killing, is just part of the Cambodian story.

Nearly a quarter of the population died under their rule, through a combination of starvation, medical neglect, overwork and ­execution when the group held power in 1975-79.

Many have criticised the slow justice, and its cost. The tribunal, formally known as the Extraordinary Chambers in the Courts of Cambodia and comprising Cambodian and international jurists, began operations in 2006.

It has since spent more than $200 million (£120m).