Rwandans told 'never again'
Rwanda has long complained that other nations stood idle when the massacres erupted in April 1994, mostly of people from the Tutsi minority but also moderates among the Hutu majority.
"Behind the words 'never again' there is a story whose truth must be told in full," the president told attendees, who watched performers dressed in grey symbolically re-enacting some of the horrors.
Rwandans carried out the genocide, "but the history and root causes go beyond this beautiful country", he said.
"No country is powerful enough, even when they think they are, to change the facts," he said in an apparent swipe at France. In a speech in English and the Kinyarwanda language, he added in French: "Facts are stubborn," drawing applause.
Kagame, a Tutsi who led an army into Kigali in 1994 to halt the genocide, has in the past accused France of training and arming Hutu extremists. Recently he had seemed to have dropped the issue and ties had been slowly improving.
But in an interview in a weekly journal published this month he said France and former colonial power Belgium had a "direct role" in the genocide. In response, France said it would not send a ministerial delegation.
On Monday, France's foreign minister in 1994, Alain Juppe, demanded President Francois Hollande defend France's honour against the accusations. "Rwanda's regime has made a habit of repeatedly falsifying history," Juppe told reporters.
Hollande avoided reference to the row, saying in a statement: "On this day of commemoration, France stands by all Rwandans to honour the memory of all the victims of the genocide."