The trial of a former Rwandan official accused of being a main perpetrator of the genocide is due to begin at the UN war crimes tribunal in Tanzania.

Colonel Tharcisse Renzaho, former prefect of the Rwandan capital, Kigali, faces charges of genocide and complicity in genocide.

Some 800,000 people, most of them Tutsis, were killed by Hutu extremists during the massacres in 1994.