The UN tribunal for Rwanda on Wednesday handed life sentences to two former heads of the ex-ruling party for genocide crimes committed in 1994.

"After considering the gravity of the crimes for which Ngirumpatse has been found guilty as well as all the attenuating and aggravating circumstances, the court has the discretion to impose a single sentence and has decided to do that," presiding judge Dennis Byron said.

"The court unanimously sentences Matthieu Ngirumpatse to life in prison," Byron said.

The judge then handed down the same sentence to Edouard Karemera, the former deputy leader of Ngirumpatse's National Revolutionary Movement for Development.

The two men were sentenced for genocide, crimes against humanity and war crimes, for not having prevented or denounced crimes committed in 1994 by the party's youth wing militia, the Interahamwe.

An estimated 800,000 people, mostly minority Tutsis, were killed in the genocide.

The ruling found that the "joint criminal enterprise" aimed at exterminating Tutsis took shape starting April 11.

That day and the next, the ruling said, arms were delivered to Interahamwe militia at Kigali's Diplomates hotel with the approval of Ngirumpatse.

"At that point in the genocide it could be assumed the weapons were going to be used to kill Tutsis," the panel of three judges wrote in their ruling.

"Starting on that date a joint criminal enterprise saw the day with the participation of figures from the interim government, political leaders, Interahamwe chiefs and influential businessmen," the ruling went on, saying the joint criminal enterprise went on until mid-July 1994.

"The court concludes that the rapes and the sexual crimes carried out on Tutsi girls and women by soldiers and militia, including the Interahamwe, are a natural and predictable consequence of the joint criminal enterprise seeking to destroy the Tutsi ethnic group," the judges said.

Ngirumpatse was chairman of the party of the late president Juvenal Habyarimana, and Karemera was his deputy.