President Kagame attended a symbolic burial at Nyanza
Rwandan President Paul Kagame has accused the international community of cowardice during a speech marking the 15th anniversary of Rwanda's genocide.
He told a rally of 20,000 people in the capital, Kigali, UN troops abandoned their posts without firing a shot.
Thousands of candles were lit at the stadium, spelling out the word "hope".
Mr Kagame also led commemorations at Nyanza, where more than 5,000 people were slaughtered after peacekeepers pulled out.
Some 800,000 people were killed within 100 days by ethnic Hutu militia after the assassination of the president.
The genocide began when Juvenal Habyarimana's plane was shot down on 6 April 1994 and came to an end when Tutsi-led rebels under the current president took control.
The massacre at Nyanza took place after Belgian troops withdrew following a Rwandan militia attack that claimed the lives of 10 peacekeepers on 7 April that year.
The BBC's Geoffrey Mutagoma in Kigali says the site of the former peacekeepers' base is seen as a symbol of the UN's failure 15 years ago.
President Kagame said: "We are not like those who abandoned people they had come to protect," reported AFP news agency.
"They left them to be murdered. Aren't they guilty? I think it is also cowardice. They left even before any shot was fired.
"We are not cowards. They [the international community] are part of that history and the root causes of the genocide."
He laid a wreath at the hill site in Nyanza and lit a torch in memory of the victims.
The BBC's Karen Allen in Kigali says children born after the genocide came to lay flowers with adults, many of whose entire family were wiped out in the genocide.
Our correspondent says Rwanda has taken many practical steps to build bridges between the Tutsi and Hutu communities.
Some of the most senior perpetrators of the violence have faced a special tribunal in Tanzania although scores of key suspects remain at large.
Although the younger generation is spear-heading efforts at reconciliation, many older people are finding it harder to forgive, she says.
Mary Kayitesi Blewit lost 50 members of her family in 1994 and went on to become the founder of the Rwandan Genocide Survivors Fund.
RWANDA'S 1994 GENOCIDE
Rwandan Hutu President Habyarimana's plane shot down
An estimated 800,000 Tutsis and moderate Hutus killed
Tutsi-led rebel group RPF captures Rwanda's capital Kigali
Two million Hutus flee to Zaire, now DR Congo
She told the BBC's Network Africa that her younger brother died in the first week of the genocide and some of those responsible were known to the family.
"It was a very close neighbour actually. In fact two were neighbours in the nearest neighbourhood. The rest we didn't know. They were groups of people that used to come together and he was killed near his house."
What concerns her now, she says, is the lack of justice.
"What's bothering me currently is that everyone else apart from survivors is talking about forgiveness and nobody is talking about justice.
"There is absolutely no justice and therefore for me there is no forgiveness."