A United Nations-backed tribunal in Cambodia says four ex-Khmer Rouge leaders charged with genocide in the deaths of up to 2 million people will first face prosecution individually for crimes against humanity, in a move to speed up proceedings.

The tribunal move, announced Thursday, separates the trials of the four senior surviving members of the ultra-Maoist Khmer Rouge, which ruled the Southeast Asian nation from 1975 to 1979. The defendants, all of whom deny the charges, include nominal Khmer Rouge head of state Khieu Samphan and Nuon Chea, described as the regime's chief ideologue. Khmer Rouge Foreign Minister Ieng Sary and his wife Thirith also face the same charges.

Khmer Rouge leader Pol Pot died in 1998.

A tribunal statement Thursday said the division aims to safeguard the interests of victims, as the long-awaited prosecutions in a single trial could take years, and the elderly defendants – all older than 78 – are likely to die before verdicts are reached. The tribunal statement estimated it could take as long as 10 years to reach a verdict in a single trial.

No timetable was announced for the start of the separate trials.

In a landmark first trial last year, the tribunal sentenced former Khmer Rouge lieutenant Kaing Guek Eav, better known as Duch, to 30 years in prison for his role as chief of the notorious Tuol Sleng torture prison during the regime's rule. The tribunal later reduced the sentence to 19 years, granting Duch credit for time already served while awaiting trial. Prosecutors have appealed the reduced sentence and are awaiting a tribunal ruling.