Cambodia's former Khmer Rouge president, Khiew Samphan, was charged on Friday with genocide by the UN-backed war crimes court in Phnom Penh.

He is the most senior Khmer Rouge leader to face charges in connection with the deaths of 1.7 million people during the 1975-79 "Killing Fields" reign of terror.

Similar charges of genocide were issued on Wednesday against "Brother Number Two" Nuon Chea and former Foreign Minister Ieng Sary for their alleged roles in the slaughter of Cambodia's ethnic Vietnamese and Cham Muslim minorities during the Khmer Rouge regime.

All three have already been charged with war crimes and crimes against humanity, along with two other former leaders of the Khmer Rouge, who pursued a bloody agrarian revolution from 1975 to 1979 under the leadership of Pol Pot, who died in 1998.

It comes three weeks after the end of the first trial of a senior Khmer Rouge cadre. Kaing Guek Eav, better known as Duch, was accused of overseeing the torture and murder of more than 14,000 people. A verdict in that case is expected by March.

Khieu Samphan (78), a French-educated guerrilla leader, was arrested in 2007. He has portrayed himself as a virtual prisoner of the regime and denied knowledge of any atrocities.

David Chandler, an authority on the Khmer Rouge at Melbourne's Monash University, said the genocide charges further complicated a case that is already so complex and politicised it may never go to trial.

Delaying the trials

He said the new charges may inadvertently help the defence if they delay proceedings. The four remaining suspects awaiting trial are elderly and in poor health. There is concern they may die before facing their victims in court.

"It's going to be very helpful for the defence to throw up a big smokescreen," Chandler said.

The United Nations defines genocide as "acts committed with the intent to destroy, in whole or in part, a national, ethnical, racial or religious group".

Some analysts argue this does not apply to the Khmer Rouge because they committed atrocities against political enemies, mostly from their own dominant Khmer ethnic group.

But advocates of the charges say the regime's enemies also included ethnic Vietnamese and Cham who rose up and rebelled against the regime.

(Source: Reuters)