Burundi's army says that 79 "enemies" and eight soldiers were killed during the bloodiest day in months of unrest on Friday (local time), which left the streets of the capital strewn with bodies, many bearing gunshot wounds.
The violence began with coordinated attacks by unidentified gunmen on three military installations, which triggered a fierce riposte from the security forces.
Several witnesses described the police and army going door-to-door in opposition strongholds in the capital Bujumbura, dragging out young men and executing them.
Army spokesman Colonel Gaspard Baratuza on Saturday said all those killed were either "enemies" of the state, soldiers or policemen.
"The final toll of the attacks yesterday is 79 enemies killed, 45 captured and 97 weapons seized, and on our side eight soldiers and policemen were killed and 21 wounded," Baratuza said.
The army had given a much lower toll after the assault on Friday on two military bases and a military training college, saying that 12 rebel gunmen had been killed and 21 captured in the attacks.
But on Saturday morning horrified residents of different neighbourhoods awoke to find at least 39 corpses scattered in the streets.
"Fighting continued into the night and the corpses found in these neighbourhoods this morning are enemies," Baratuza declared.
Several witnesses accused the security forces of extrajudicial killings, describing officers breaking down doors in search of young men and shooting them at close range.
Some of the victims had their arms tied behind their backs, they said.
The army spokesman declined to comment on the details of the fighting and deaths.
One witness in Nyakabiga, a hotspot of anti-government protest in recent months, described the victims as "kids" and said they had been shot execution-style "through the top of the skull".
A resident of Musaga, close to the military college that was among the sites attacked on Friday, said there were more than a dozen corpses in the streets. "I have counted 14 dead bodies with my own eyes," he said, blaming "soldiers and police" for the killings.
The government collected bodies from the streets of Bujumbura on Saturday, with sources saying they were swiftly buried in mass graves in the afternoon "to prevent the spread of disease."
But some residents said they suspected the authorities of trying to hide evidence of a massacre perpetrated by the security forces, a view echoed by a European diplomat.
"There are dozens of bodies but the authorities are trying to make them disappear," said the diplomat, who spoke of "dozens of bodies in other protest districts, such as Mutakura and Cibitoke" on top of those in Nyakabiga.
The fighting was the worst outbreak of violence since a failed coup in May, sparked by President Pierre Nkurunziza's bid for a third term in office, which he later won in disputed elections in July.