The first day of the trial of four former Rwandan army officers accused of planning the massacre of 500,000 people got off to a rocky start Tuesday, with the defendants boycotting proceedings.

UN prosecutors said the four accused masterminded the massacre of Tutsi civilians and politically moderate Hutus by Hutu extremists during the 1994 civil war in Rwanda.

The four said their rights were violated because they had not been given French translations of key prosecution documents. The international tribunal ruled the UN could make opening statements, but could not call witnesses until documents relating to their testimony were translated.

Men "perpetrators of genocide," UN says

The four are "among the principle perpetrators of the genocide," UN top prosecutor Carla Del Ponte told the court. They "unleashed a legion of ferocious demons" that killed, raped and maimed "every victim they could," lead prosecutor Chile Eboe-Osuji said.

But defence lawyer Kennedy Ogetto said the men were fighting Tutsi rebels at the time of the genocide and were not involved in the killings.

He called the prosecution theories nonsense, and said the opening statements were politically motivated.

The massacres took place amidst a Tutsi rebellion, which succeeded when they captured Kigali, the capital. That ended the killing.

The four men fled, but were captured in Cameroon. They are jailed in Arusha, the northern Tanzanian town where the tribunal is based.

The four are Col. Theoneste Bagosora, Lt.-Col. Anatole Nsengiyumva, Maj. Aloys Ntabakuze and Brig.-Gen. Gratien Kabiligi.

All have pleaded not guilty to charges of rape, genocide and crimes against humanity.