A U.N.-backed war crimes tribunal is due to deliver its first verdicts Thursday in a historic case against the only two living leaders of Cambodia's Khmer Rouge regime on trial.

The verdict comes three and a half decades after the group's genocidal rule ended, leaving nearly 2 million people dead.

Khieu Samphan, the regime's 83-year-old former president, and Nuon Chea, its 88-year-old chief ideologue, face sentences ranging from five years to life for their actions in the 1970s terror.

Both men, in dire health, have denied any wrongdoing.

The case began in 2011.

It covers the forced exodus of millions of people from Cambodia's towns and cities and a mass killing.