"They were detained Wednesday morning after an inquiry carried out in Belgium and at the request of the prosecution," Leen Nuyts, spokesman for the prosecutor’s office, told AFP.

They were then charged with genocide, war crimes and crimes against humanity and placed in preventive detention, she said.

A court will rule Monday on whether they can be provisionally released.

Nuyts did not name the men, saying only that one was born in 1975 and the other in 1959, that they had acquired Belgian nationality and that they faced prosecution for "acts committed during the 1994 genocide."

An estimated 800,000 Rwandans, chiefly members of the minority Tutsi ethnic group, are estimated by the United Nations to have died in the genocide.

The Rwandan newspaper New Times has identified the men as Ernest Gakwaya, nicknamed "Camarade" (Comrade) and Emmanuel Nkunzuwimye, known as "Bomboko".

Gakwaya was well known in Nyamirambo, a working class area of the capital Kigali, and in 1994 "was one of the (majority Hutu ethnic group) interahamwe (militias) most active during the genocide," the newspaper said, quoting "survivors.".

Emmanuel Nkunzuwimye "was considered as close to Jean-Marie Vianney Mudahinyuka, sentenced to 19 years in prison in Rwanda," it claimed.

Belgium has already held four trials in connection with the genocide.

At the end of 2009 Ephrem Nkezabera, nicknamed "the genocide’s banker", was given a 30-year term by a Brussels court.

The same court had already handed down long jail terms on two nuns, a university teacher and an industrialist in 2001, two businessmen from the north of Rwanda in 2005 and an ex-major in July 2007.

It acted under the "universal competence" of Belgian courts to try those suspected of being responsible for alleged crimes against humanity.