Burundian police say 21 people been wounded in a grenade attack in the Burundian capital, nine of them seriously.

Burundian police spokesman Pierre Nkurikiye said the attack occurred in the Buyenzi neighborhood of Bujumbura on Thursday afternoon in a crowded area where car parts are sold.

Senda Selemani, who witnessed the blast, said the grenade was concealed in a bag that was thrown into the crowd by two men on a motorcycle.

Grenade and gun attacks are common in Bujumbura amid unrest stemming from the president's decision last year to seek a third term in office despite violent protests.

Hundreds of people have been killed in Burundi since April 2015, according to the U.N.