PARIS French authorities on Thursday arrested a Congolese general and put him under formal investigation for crimes against humanity over the 1999 disappearance of hundreds of refugees, a judicial source said.
General Norbert Dabira was later set free but put under "strict judicial control", the source said.
Human rights campaigners say soldiers loyal to President Sassou Nguesso of the Republic of Congo tortured and then killed 350 refugees after they returned home from the Democratic Republic of Congo, on the other bank of the Congo river.
French authorities first opened an investigation into the alleged massacre in 2001.
Six years ago, when a French court reopened the investigation, the Republic of Congo called the move a "grave affront to its sovereignty" and warned it could seriously harm ties.
A Congolese tribunal in 2005 acquitted 15 suspects, including several army generals, of charges of genocide, crimes against humanity and other offences relating to the incident.
But the tribunal recognized that people had disappeared, and awarded compensation to the families of each of around 100 victims who have been identified.
Under French law, a formal investigation means a judge consider there is evidence of a suspect's probable implication in a crime and is an important step towards a trial.
Dabira is currently the Republic of Congo's High Commissioner in charge of the reintegration of ex-combatants.
(Reporting by Chine Labbe and Gerard Bon; writing by Ingrid Melander; editing by Andrew Roche)