Democratic Republic of Congo has arrested a former mayor accused of orchestrating a massacre that killed tens of thousands of people during Rwanda's 1994 genocide, Rwanda's prosecutor general said on Thursday.

Ladislas Ntaganzwa, who headed the commune of Nyakizu in southern Rwanda, was indicted in 1996 and is accused of genocide, direct and public incitement to commit genocide as well as extermination, murder and rape, Prosecutor General Richard Muhumuza said in a statement.

"The National Public Prosecution Authority is pleased to announce the recent arrest of Ladislas Ntaganzwa, one of the last fugitive suspects sought by the International Criminal Tribunal for Rwanda," Muhumuza said.

The tribunal's indictment, updated in 2012, accuses Ntaganzwa of plotting to exterminate Rwanda's Tutsi population and personally ordering the massacre of more than 20,0000 Tutsi civilians in a church parish in April 1994. The United States offered up to $5 million for information leading to his arrest.

Also in a statement on Thursday, the U.N. Mechanism for International Criminal Tribunals urged Congo to immediately transfer Ntaganzwa to Rwanda for trial.

A U.N. source said the arrest took place in the town of Nyanzale in North Kivu province, a region where many perpetrators of the genocide fled after they were chased from Rwanda by Tutsi rebels.

Hutu militias slaughtered some 800,000 Tutsis and moderate Hutus in Rwanda between April and June 1994. More than 20 years later, Rwanda is still pursuing the perpetrators at home and internationally. The tribunal says it has indicted 93 people so far.