The killing spree, which lasted 100 days before the Rwandan Patriotic Front (RPF) rebel militia took Kigali in July 1994, claimed the lives of 800,000 people, largely Tutsis but also moderate Hutus.

The tiny nation has since found its footing under the rule of President Paul Kagame, who led the RPF, but the scars of the violence remain, leaving a trail of destruction across Africa's Great Lakes region.

In keeping with tradition, the ceremonies on April 7 -- the day Hutu militias unleashed the carnage in 1994 -- began with Kagame lighting a remembrance flame at the Kigali Genocide Memorial, where more than 250,000 victims are believed to be buried.

Sunday's events mark the start of a week of national mourning, with Rwanda effectively coming to a standstill and national flags flown at half-mast.