The four men, all former senior military commanders in the Rwandan army, are accused of genocide, crimes against humanity and war crimes.
Tribunal spokesman Kingsley Moghalu told the news conference these men are believed to have planned the genocide in Rwanda.
"These four officers are believed by the prosecutor to have played a masterminding role in the genocide. They are alleged to have worked at the very highest levels of the Rwandan army to concoct the plan of the genocide and to have worked together with extremist Hutu politicians who were in power in Rwanda at the time to implement this plan".
The men on trial are Colonel Theoneste Bagosora, Lieutenant-Colonel Anatole Nsengiyumva, Major Aloys Ntabakuze and Brigadier-General Gratien Kabiligi.
Colonel Bagosora is the most senior of the four accused. As the head of the cabinet in the ministry of defense, he was in charge of the Rwandan army when the genocide began.
Colonel Bagosora, a Hutu, is accused of being vehemently opposed to a power-sharing plan aimed at ending Rwanda's four-year-old civil war. Under the plan, Rwanda's ethnic Hutu majority would have been forced to share power with the Tutsi minority. Instead, Colonel Bagosora allegedly decided to exterminate the Tutsi.
The event that sparked the genocide was the death of Rwandan President Juvenal Habyarimana in a plane crash in April 1994.
Following the president's death it is alleged that Colonel Bagosora decided to form an interim government. But first Prime Minister Agathe Uwilingiiyimana had to be eliminated.
Mr. Mogahalu said the four military officials are also accused of masterminding her death.
"One of the things that happened shortly after the plane crash, and some of the people that are charged with Bagosora are alleged to be part of that whole affair, is that Agathe, the prime minister, was very quickly rounded up, sexually assaulted, tortured and assassinated in cold blood".
The trial begins next week (Tuesday) at the court of the International Criminal Tribunal for Rwanda in the Tanzanian town of Arusha. It is expected to last two years. If convicted, Colonel Bagosora and his colleagues face life sentences.