Rwandan President Paul Kagame will light a national flame of mourning Monday at a ceremony marking 20 years since the start of a genocide that left 800,000 people dead.
The flame will burn for 100 days, equal to the amount of time ethnic Hutu militias rampaged across the country in 1994, killing Tutsis and moderate Hutus after the death of Rwanda's president in a plane crash.
Heads of state and dignitaries from the United States, Britain and East African nations are expected to take part in the ceremony in Kigali.
United Nations Secretary-General Ban Ki-moon said Sunday he will reaffirm the international community's commitment that such atrocities "should never happen in human history."
He also praised Kagame's leadership, saying the president has "made shining examples" of socioeconomic success, democracy and human rights.
President Barack Obama said in a statement marking the anniversary that the genocide was a "deliberate and systematic effort" by humans to destroy other humans. He said when faced with hatred and cruelty, people must remember their shared humanity, choose compassion and "never be indifferent."
Obama also said we must remember the world's failure to respond to the situation more quickly.
In the early 1990s, the United Nations had several thousand peacekeepers in Rwanda who have been criticized for their inability or unwillingness to stop the genocide, despite warnings.
In 1999, an independent inquiry ordered by then-U.N. chief Kofi Annan said the inability to prevent or stop the genocide "was a failure by the United Nations system as a whole." The report said member states did not have the will to act with assertiveness, and that there were "serious mistakes" made with the resources that were available to the U.N. mission in Rwanda.
At an international forum on genocide in Kigali on Sunday, Rwanda's government reiterated remarks that France played a "direct role" in the genocide.
Foreign Minister Louise Mushikiwabo said France has "wronged" Rwanda by being partially responsible for the genocide. She said relations between France and Rwanda cannot be repaired if Rwanda has to accept the French version of events.
She echoed Kagame's remarks that France and Belgium played what he called a "direct role" in the political preparation for the genocide. The president's remarks led France to cancel plans to attend the ceremonies this week.
France has denied any responsibility for the genocide and says the accusations go against the reconciliation process between the two countries.
In Rome, Pope Francis, the head of the Roman Catholic Church, said Sunday he wanted to express his "paternal closeness to the Rwandan people" and encouraged them to continue the process of reconciliation "with determination and hope."