Judges in Phnom Penh delivered the ruling on Thursday. The 88-year-old Nuon Chea, better known as Khmer Rouge leader Pol Pot's Brother Number Two, and former head of state Khieu Samphan, 83, were given life sentences.

Prosecutors had sought the maximum life terms for the defendants for their roles in a regime which left an estimated 1.7 million people dead during the "Killing Fields" era of the Khmer Rouge regime from 1975-1979.

Victims died from starvation, overwork or were executed in the government's attempt to create an Agrarian utopia.

The two men, who are in poor health and deny the charges, can appeal the verdict. However, judge Nil Nonn said the gravity of the crimes meant they "shall remain in detention until this judgement becomes final."

The hybrid national and United Nations tribunal was set up in 2006 to try the worst crimes that occurred under Pol Pot's regime. To date, the court case has cost about $200 million (149.3 million euros), which has been largely funded by donor countries such as Japan and Germany.

Since the trial began one person has been convicted. The head of the S-21 torture center, Kaing Guek Eav - alias Duch - received life imprisonment for overseeing the deaths of 15,000 people.

Observers and victims had been concerned that the ageing Khmer Rouge leaders would not survive to see the end of the trials.

Former regime Foreign Minister Ieng Sary died aged 87 last year while on trial for war crimes, while his wife was freed from jail in September 2012 after being ruled unfit for trial due to dementia.

dr,hc/lw (dpa, AP, AFP)