A French newspaper says an official report has blamed Rwandan President Paul Kagame for a rocket attack that triggered the genocide 10 years ago.
Mr Kagame has presidential immunity
Le Monde says French police have concluded that Mr Kagame gave direct orders for the rocket attack on then President Juvenal Habyarimana's plane.
Mr Kagame was head of the rebel Rwandan Patriotic Front (RPF) at the time.
An RPF spokesman has dismissed the allegations and there has been no official confirmation of the report.
The death of Mr Habyarimana, a Hutu, triggered the 1994 genocide in Rwanda in which some 800,000 people died, most of them Tutsis.
Burundi's then President Cyprien Ntaryamira was also killed in the rocket attack.
Le Monde says the accusation against Mr Kagame is contained in a 220-page report drawn up by police acting for France's leading anti-terrorist judge, Jean-Louis Bruguiere.
The police are investigating the deaths of several French citizens on the plane.
The newspaper says the report was based on interviews with hundreds of witnesses, including one man who allegedly belonged to the assassination squad.
It says that according to the report, the aircraft was downed on the clear instructions of Mr Kagame, who was then in charge of the mainly-Tutsi RPF.
Mr Habyarimana's death in the crash led to the genocide of Tutsis, which only ended when Mr Kagame took power in Rwanda.
Mr Bruguiere has not yet handed the report over to the French prosecutor's office.
A government spokeman in Rwanda rejected the accusation, which he blamed on the history of poor relations between Mr Kagame and Paris.
Correspondents say relations between France and Rwanda have been tense for many years because of accusations that France - which was President Habyarimana's main backer - connived in the genocide.
France denies the allegation.