Rwanda's president said the international community had “betrayed us all” on the 30th anniversary of the 1994 genocide that killed around 800,000 people.
President Paul Kagame addressed dignitaries and world leaders gathered in Rwanda's capital Kigali to commemorate the bloodshed.
“Rwanda was completely humbled by the magnitude of our losses,” he said.
“And the lessons we learned are written in our blood.”
On this day in 1994, Hutu extremists began a 100-day killing spree, slaughtering members of the Tutsi minority and moderate Hutu factions.
The predominantly Tutsi forces that came to power after the genocide are said to have killed thousands of Hutus in Rwanda in retaliation.
On Sunday, Kagame and a group of senior officials laid wreaths at a mass grave at the Kigali Genocide Memorial, where more than 250,000 victims are believed to be buried. The president also lit a memorial fire.
In a speech afterwards, Kagame thanked African countries, including Uganda, Ethiopia and Tanzania, for hosting Tutsi refugees and helping end the genocide.
“Many of the countries represented here also send their sons and daughters to serve as peacekeepers in Rwanda,” he said.
“Those soldiers did not let Rwanda down. It was the international community that let us all down. Whether out of contempt or cowardice.”
The failure of other countries to intervene has been a source of lingering shame.
Former US President Bill Clinton, one of the visiting leaders in attendance, called the genocide the administration's greatest failure.
French President Emmanuel Macron acknowledged in a video message recorded for the memorial that France and its allies could have stopped the genocide but did not have the will to do so. .
France, led by then-President François Mitterrand, was closely allied with the Hutu-led government of Juvenal Habyarimana before the killing, but Rwanda said France ignored or overlooked warning signs and trained the militias that carried out the attack. He is accused of doing something like that.
French Foreign Minister Stephane Séjournet attended the ceremony in Kigali on Sunday in Macron's place. Other visiting dignitaries include Ethiopian Prime Minister Abiy Ahmed, South African President Cyril Ramaphosa and Israeli President Isaac Herzog.
Sunday's events mark the beginning of a week-long period of mourning across Rwanda. Music, sports and movies will not be broadcast on radio or television, and the national flag will be flown at half-mast.
According to the BBC reporting team, the streets of Kigali are unusually quiet, with no traffic, many shops closed and few pedestrians.
The genocide began on the night of April 6, 1994, when Hutu president Juvenal Habyarimana was assassinated and the plane he was on was shot down.
Hutu extremists blamed the Tutsi RPF rebels and launched an organized genocide campaign.
Their victims were shot, beaten, or mutilated to death in murders fueled by vicious anti-Tutsi propaganda spread on television and radio.
Thousands of Tutsi women were kidnapped and held as sex slaves.
After 100 days of violence, Kagame's RPF rebel militia succeeded in overthrowing the Hutu authorities and ending the genocide.
Human rights groups claim RPF fighters killed thousands of Hutu civilians as they seized power and many more after pursuing Hutu militia members who had fled to the Democratic Republic of Congo. ing. RPF denies this.
The scars of the violence remain, and new mass graves continue to be discovered across the country.
Dozens of senior officials from the previous government were convicted of genocide, all of them Hutus.
Regional courts, known as gacacas, have been established within Rwanda to speed up the prosecution of the hundreds of thousands of genocide suspects awaiting trial.
Rwanda says hundreds of suspects remain at large, including in neighboring countries such as the Democratic Republic of Congo and Uganda.
President Kagame has been praised for transforming the small, devastated country he inherited through policies that fostered rapid economic growth.
But his critics say he does not tolerate dissent and that several opponents have died unexplained deaths at home and abroad.
Genocide remains a highly sensitive issue in Rwanda, and it is illegal to talk about ethnicity.