One of nine top fugitive Rwandan genocide suspects, a former mayor accused of slaughtering thousands and organising mass rapes in 1994, has been arrested, the UN has said.

Ladislas Ntaganzwa is indicted for genocide and crimes against humanity, "for the massacre of thousands of Tutsis at various locations.... he was also alleged to have orchestrated the rape and sexual violence committed against many women," the UN-backed Mechanism for International Criminal Tribunals (MICT) said in a statement received Thursday.

Ntaganzwa, 53, who was arrested in Democratic Republic of Congo on Wednesday, is expected to face trial in Rwanda.