At least 400 detained, rights group says, after protests sparked by endorsement of president as candidate for June poll.
Three people, including two policemen, were killed and several people wounded in a grenade attack in the capital of Burundi, police and witnesses said.
The deaths on Friday came in an attack in the Kamenge district of Bujumbura, which has been rocked by protests at the president’s bid to seek a third term in office.
Police director general General Andre Ndayambaje told AFP news agency that two officers were killed and one was wounded, while a local resident said a civilian also lost his life and two others were wounded.
A similar attack in the centre of the capital of the small central African nation wounded three policemen, the general said.
A senior police officer, who requested anonymity, said police patrolling on foot in Kamenge were attacked with a grenade and a police vehicle was also hit with a grenade.
The local resident said the grenade attack was followed by automatic gunfire.
One policeman died on the spot and another was wounded in the legs, he said.
Minutes later, a grenade exploded under the car of the local police chief who had arrived on the scene. He got out but was killed by gunfire.
According to the resident, a civilian was also killed in the shooting and a woman and a child wounded by the second grenade.
A reporter at the scene saw two small craters a few hundred metres apart and traces of blood in the vicinity.