Gunmen opened fire inside a bar in western Burundi late Sunday, killing more than 20 people in the country's deadliest attack this year.

The attack happened in Gatumba, about 15 kilometers west of the capital, Bujumbura.

One official, Bujumbura province governor Jacques Minani, put the death toll at 36.

It was not immediately clear who was responsible for the attack.

Burundi has been relatively peaceful since the rebel group Forces for National Liberation laid down its arms in 2009 after 20 years of insurgency.

But recurring attacks have raised fears of a return to conflict. The government has blamed a number of attacks this year on armed bandits.