The UN court for Rwanda handed former army chief Augustin Bizimungu a 30-year jail term for his role in the 1994 genocide, including for calling for the murder of minority Tutsis.
It also jailed two senior officers for ordering their men to assassinate the prime minister at the start of the 100-day killing spree, when they also murdered 10 Belgian UN troops protecting her.
The International Criminal Tribunal for Rwanda (ICTR) convicted the head of the paramilitary police at the time, Augustin Ndindiliyimana, of genocide crimes but ordered his release as he had already spent 11 years in jail.
The main survivors' organisation condemned the ruling on Ndindiliyimana as too light.
He and Bizimungu are among the most senior figures to be tried by the Tanzania-based tribunal for the genocide in which 800,000 people, mostly Tutsis, were killed.
Complete control
The court found Bizimungu had complete control over the men he commanded, who were involved in the massacres that started in the night of April 6, 1994.
It also found him guilty of making a speech on April 7, 1994, several days before he was made army chief, that called for the killing of ethnic Tutsis.
The court did not find Ndindiliyimana guilty of committing any crimes himself and said he only "limited control" over his men and was opposed to the killing.
Ndindiliyimana was arrested in January 2000 in Belgium and Bizimungu in Angola in 2002.
Rwanda's Prosecutor General Martin Ngoga told AFP the army chiefs could have prevented the genocide had they wanted to.
"Sentencing the army officers is particularly important because if the army had wanted, genocide would not have occurred. The army deviated from it's role," he told AFP.
Others jailed
The tribunal sentenced two other senior officers to 20 years in jail for war crimes and crimes against humanity for ordering the murder of prime minister Agathe Uwilingiyimana.
The judges found the officers instructed an armoured unit to kill Uwilingiyimana and made no attempt to punish the soldiers who also killed the Belgian UN Blue Helmets protecting her.
The killing of the Belgians triggered the withdrawal of the UN force stationed in Rwanda.
The officers are Major Francois-Xavier Nzuwonemeye, the commander of the reconnaissance battalion, and captain Innocent Sagahutu, a squadron commander in the same unit.
Nzuwonemeye was arrested in France in 2000 and Sagahutu was detained in Denmark two years later.
The main genocide survivors' association criticised the term handed down to Ndindiliyimana, which would essentially see him freed, and demanded an appeal.
"It's a well-known fact that man helped plan the genocide in Kigali, Butare and elsewhere," said Janvier Forongo, secretary general of the group called Ibuka.
"Eleven years is not enough in view of the gravity of the crimes he committed," he said.
The cases of the four men had been adjourned since June 2009 when prosecutors requested life sentences for all of them but defence lawyers asked for their acquittal.
The long-running case is known as the Military II trial.
In the Military I trial, Colonel Theoneste Bagosora, presented by the prosecutor as the brains behind the genocide, was sentenced to life in prison in December 2008 along with two other senior military figures.
Bagosora appealed but the appeal verdict has yet to be handed down.
The ICTR, based in the northern Tanzanian town of Arusha, was established in late 1994 to try the perpetrators of Rwanda's genocide which claimed some 800,000 lives in a span of 100 days.
It is tasked only with trying those who bear the greatest responsibility for the genocide. Less senior officials and ordinary citizens accused of taking part have been tried in Rwanda.
