Riyadh, Saudi Arabia: A Saudi policeman was killed Tuesday and three others injured by an explosive device in a flashpoint Shiite-dominated city, the interior ministry said.

The policemen were on patrol in the early morning in the Qatif area in Saudi Arabia's Eastern Province when the device blew up, the ministry said, calling the incident a "terrorist" attack.

On June 11 a homemade explosive device killed a senior policeman and wounded two officers in Qatif.

That blast came almost two weeks after a car exploded in the restive district killing its two occupants. The interior ministry said the pair were wanted suspects.

Eastern Province, where most of Saudi Arabia's Shiite minority live, has been rocked by unrest since 2011.

Authorities have blamed the unrest on "terrorists" or drug traffickers.