Gunmen have opened fire in a bar in western Burundi, killing more than 20 people in the deadliest attack in the country this year.

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

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.

The government has blamed a number of attacks this year on armed bandits, and the violence has raised fears of a return to conflict.