An official in Burundi says four people died and at least 30 were wounded in a grenade attack on a bar in the country's northern region of Ngozi.

Ngozi's Governor Claude Nahayo said Monday three people have been arrested following the overnight attack in which two grenades were used.

Nahayo says the motive is not clear. Eight police officers were wounded over the weekend in grenade attacks in Bujumbura, the capital. The attacks fall into a pattern of pre-election violence. Ahead of the 2010 presidential polls there were at least 60 grenade attacks. In recent weeks, Bujumbura has been rocked by protests following the April announcement that President Pierre Nkurunziza will seek a third term in office.