Burundi's army says it has killed 13 fighters from the last active rebel group, the National Liberation Forces (FNL), outside the capital, Bujumbura.
Hundreds of thousands have fled the Burundi conflict over the years
The killings took place after the army learnt of the presence of a 20-strong group, including new recruits.
An army spokesman denied allegations the rebels had been shot in cold blood.
Peace talks in Tanzania between the government and rebels aimed at ending the 12-year civil war have been postponed until next week.
The chief mediator, South African Security Minister Charles Nqakula, said more discussion was needed before they could be resumed.
He said the rebels had dropped their demand for the dissolution of the Burundian army.
Army spokesman Adolphe Manirakiza said at least one soldier was wounded during the raid late on Thursday which happened in the rural area of Muberure near Bujumbura.
Since independence in 1961, Burundi has been plagued by tension between the dominant Tutsi minority and the Hutu majority.
In the peace process that brought President Pierre Nkurunziza to power last year, the previously Tutsi-dominated army has been split equally between Tutsis and Hutus.
More than 300,000 people have died in the war sparked in 1993 by the assassination of Burundi's first Hutu head of state and democratically-elected president, Melchior Ndadaye.