Following a challenge from the plaintiffs, the French appeals court has now ordered investigators at Paris' crimes against humanity division to reopen their Rwanda genocide probe after finding procedural mistakes, a source familiar with the case told AFP.
Specifically, they had failed to warn the case would be closed just weeks after allowing new documents - a summary of historian Vincent Duclert's report into the Bisesero incident - to be taken into evidence.
"We're again headed for months or even years of legal battles to try to secure the only thing that counts in our eyes: the end of the impunity military and political leaders have benefited from in this case," said Patrick Baudouin, president of the Human Rights League, one of the plaintiffs.
Associations and survivors of the killings of Tutsis in the Bisesero hills in western Rwanda have long accused France's "Turquoise" mission and the government of "complicity in genocide," saying the troops knowingly failed to protect victims for three days.
Hundreds of Tutsis were killed in the area between June 27 and 30, 1994.
Investigating magistrates dropped the 17-year case in September, saying there was no evidence that the French army was involved in atrocities committed in refugee camps, or that it helped the perpetrators or deliberately held off from preventing the killings.
Fierce controversy remains around France's U.N.-mandated Turquoise mission to Rwanda, which was supposed to halt the genocide.
More than 800,000 people were killed between April and July 1994 according to U.N. figures, most of them from the Tutsi minority.