Tanzania's police chief says gunmen attacked a police station in the city of Dar es Salaam, killing seven people and injuring four others.

Ernest Mangu told reporters Monday that four of the victims were police officers. Three civilians were also killed in the attack on Sunday night, although the police believe one of them was among the attackers.

Mangu said the gunmen ran away with an unknown number of firearms and ammunition.

There have been at least three attacks on Tanzanian police stations this year.

Last month a police officer was killed in an attack on a police station in the Mkuranga district of Tanzania's coastal region.