At least four people have been killed and 12 have been injured in a grenade attack on a bar in the Burundian capital, Bujumbura.
Hundreds of thousands have fled the Burundi conflict over the years
The attack took place in the city's Nyakabiga district late on Sunday.
The blast happened on the eve of talks between the government and the National Liberation Forces (FNL), the only rebel group that has not signed a peace deal.
It is not known who was responsible for the attack, which follows a series of similar incidents in Bujumbura.
"A group of unidentified people attacked La Grande Etoile [bar] last night," local administrator Richard Niyonkuru told the AFP news agency.
"They fired on the customers and then in the confusion, they threw four grenades before fleeing."
"We have at least 36 civilians wounded, a dozen of them seriously, and they are being treated in three hospitals now," he said.
A fresh round of talks between the FNL and the Burundian government was due to begin in Dar es Salaam on Monday.
Earlier attempts at peace talks between the FNL and the government have failed.
Since independence in 1961, Burundi has been plagued by tension between the dominant Tutsi minority and the Hutu majority.
Posts in the previously Tutsi-dominated army have been split equally between Tutsis and Hutus as part of a peace deal with other Hutu rebel groups.
Hutu former rebel leader Pierre Nkurunziza was last year elected president after a transition period.
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.