A Burundian army officer who had been captured by a rebel group last month was handed back to his unit on Saturday, the International Committee of the Red Cross said.
At least three armed rebel groups have emerged since a political crisis erupted in Burundi a year ago, when President Pierre Nkurunziza launched his bid for a third term in office and then won a disputed election in July.
More than 400 people have been killed in violence since April last year, worrying Western powers and regional states who fear a slide back into the kind of ethnically charged fighting witnessed during Burundi's 1993 to 2005 civil war.
Alexis Irambona was captured by a rebel group calling itself FNL, the same name as a political party in Burundi, although the party denies any links. FNL party leader Agathon Rwasa, a former rebel commander, has said he would not take up arms again.
"He was handed over from FNL to my colleagues in the Democratic Republic of Congo," Georgios Georgantas, the ICRC head of delegation in Burundi, told Reuters by telephone.
He said the handover operation began on Friday and was completed on Saturday, after he was given to the Congolese armed forces and then to his Burundi unit, in the ICRC's presence.
It was not immediately clear why the handover took place in neighboring Congo.
FNL circulated an image of Irambona a month ago on social media, showing him with his hands tied. They said at the time he was captured in a forest northeast of Bujumbura during fighting with the army.
Army spokesman Balthazar Baratuza said at that time that there had been no clashes in that area. He said Irambona was captured while on his own in the region as he rode a bicycle.
Most of the violence in the past year has been in the capital, but there have been skirmishes between armed men and the army and other members of the security forces in some rural areas and other towns or cities.
Opponents accuse Nkurunziza of violating the constitution and a peace agreement that ended the civil war by running for a third term. The president and his supporters cite a court ruling that said he could run again.
(Writing by Edmund Blair; Editing by Clelia Oziel)