French appeals judges on Friday rejected a request to reopen an investigation into the 1994 assassination of Rwanda's president Juvenal Habyarimana, which sparked the genocide that killed 800,000 people.
Families of those who died when Habyarimana's plane was shot down will bring a challenge to Friday's decision to France's supreme court, their lawyers announced.
The appeals court in Paris had been asked to revisit a 2018 decision to throw out a probe against nine members and former members of incumbent President Paul Kagame's entourage in a case that has poisoned relations between the two countries.
A plane carrying Habyarimana, from Rwanda's Hutu majority, was shot down in Kigali on April 6, 1994, triggering a 100-day killing spree targeting mainly members of the Tutsi ethnic minority, but also moderate Hutus.
The plane was struck by at least one missile as it came in to land at Kigali, also killing Burundi's president Cyprien Ntaryamira, another Hutu, on board.
A probe was opened in France in 1998 after a complaint by families of the French plane crew.