French appeals judges have 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, including Habyarimana's widow Agathe, will bring a challenge to Friday's decision to France's supreme court, their lawyers said.
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.
The investigation initially focused on allies of Kagame, a Tutsi who led the Rwandan Patriotic Front (RPF) rebel movement that came to power after defeating the Hutu regime.
Kagame, who became Rwanda's president in 2000, broke diplomatic ties with Paris between 2006 and 2009 after France issued arrest warrants for his allies.
Then in 2012, a report by French experts pinpointed the camp of Kanombe, controlled by Habyarimana's army, as the missile launch site - shifting the investigation's focus.
Kigali said the finding vindicated its belief that the attack was carried out by Hutu people who believed Habyarimana was too moderate and who opposed the Arusha peace process then underway.
As investigations dragged on, Kagame accused France in the run-up to the genocide's 20th anniversary in 2014, of having played a "direct role" in the killing.
And in November 2016, Kigali launched an inquiry into the alleged role of 20 French officials in the genocide that began hours after the plane was brought down.
France has always denied the allegations and last year, President Emmanuel Macron announced the creation of a panel of historians and researchers to look into the claims.
In December 2018, French judges dropped their probe for lack of evidence.