Rwandans observed a nationwide minute of silence Friday to mark 12 years since the former extremist Hutu government launched its slaughter of more than half a million people, mainly ethnic minority Tutsi.

President Paul Kagame and survivors of the 100-day genocide were joined by diplomats and others at the Roman Catholic Cathedral for the beginning of a national week of mourning for the Tutsi and moderate Hutu majority targeted in the 1994 killings.

"The people here were killed by Rwandans, so it is up to us to fight for the dignity that we have lost," Kagame said. "We should take most of the responsibility of what happened."

The genocide was unleashed after President Juvenal Habyarimana died when his plane was shot down as he returned home from peace talks with Tutsi-led rebels in 1994. It ended ended after rebels, led by Kagame, ousted the extremist Hutu government.

Despite the passage of time, nations still seem unwilling to commit the troops and money needed to stop mass slaughters, Juan Mendez, the U.N. special adviser on prevention of genocide, said at the United Nations in New York.

Governments have repeatedly promised "never again" in the years since the Holocaust and the Rwanda killings. They have gotten better at nurturing peace processes, but are still reluctant to do much more, he said.

"My sense is there's the same kind of wariness," Mendez said, "`Let somebody else do it' is still very much in place."

Mendez pointed to the continued violence in Sudan's Darfur region, labeled by the U.N. as the world's worst humanitarian disaster. The conflict started in 2003 and has killed tens of thousands of people, mainly through famine and disease.

A U.N. investigative commission has concluded that crimes against humanity — but not genocide — had occurred in Darfur, and the Security Council referred the case to the Hague-based International Criminal Court in March.

Mendez drew connections between Rwanda and Darfur, where the U.N. Security Council has agreed to being preparing to transfer authority for the peacekeeping force in Darfur from the African Union to the U.N.

"Debates about troop strength on the ground and about mandates of the troops on the ground are very eerily reminiscent of what happened then" in Rwanda, Mendez said.

U.S. Assistant Secretary of State for African Affairs Jendayi Frazer and American musician Quincy Jones joined in the commemorations in Rwanda.

Kagame criticized allegations that the government exploits the genocide history to silence political dissent.

"You think we are creating divisionism, this is divisionism," he said while pointing to mass graves and turning to face the foreign diplomats present. "You have no right to come and start giving other stories. Your unfounded criticism is not welcome."

Residents reburied 153 people whose remains were exhumed from pit latrines and mass graves into which they had been dumped during the slaughter. The remains of other victims were also reburied in other parts of Rwanda.