Progress has been slow at the UN-backed tribunal
A UN-backed tribunal in Cambodia has for the first time charged two former Khmer Rouge leaders with genocide.
A court official said the charges against Ieng Sary and Nuon Chea relate to their treatment of Cambodia's Vietnamese and Muslim minorities.
The two men are already in pre-trial detention charged with crimes against humanity, but it is thought their trial will not start until 2011.
Up to two million people are thought to have died under the Khmer Rouge's rule.
The two men were both high-ranking members of Pol Pot's government in the late 1970s.
A court official confirmed that the allegations were the related to the treatment of two minority groups: Cham Muslims and ethnic Vietnamese people.
The accusation of genocide carries enormous symbolic weight, says the BBC's Guy De Launey in Cambodia's capital, Phnom Penh.
WHO WERE THE KHMER ROUGE?
Maoist regime that ruled Cambodia from 1975-1979
Founded and led by Pol Pot, who died in 1998
Abolished religion, schools and currency in a bid to create agrarian utopia
Up to two million people thought to have died from starvation, overwork or execution
Researchers believe that the Khmer Rouge killed hundreds of thousands of Chams because of their religious beliefs.
Vietnamese people also found themselves enemies of a movement which emphasised its Khmer ethnicity.
Progress towards a trial for Ieng Sary, Nuon Chea and two other Khmer Rouge leaders has been slow and it is not likely to start until 2011.
The genocide charges may cause further complications, says our correspondent.
Final arguments were heard last month in the trial of Khmer Rouge prison chief Kaing Guek Eav, known as Comrade Duch, who has admitted being responsible for overseeing the deaths of 15,000 people.
Judges at the tribunal are expected to make a ruling on his verdict early next year.