Two Saudi policemen were shot dead by anonymous gunmen in Saudi city of Dammam on Oct. 25. (Xinhua/AFP Photo)

RIYADH, Oct. 25 (Xinhua) -- Two Saudi policemen were shot dead by anonymous gunmen in Saudi city of Dammam, the Saudi Interior Ministry tweeted on Tuesday.

The ministry has launched probe into the attack. And on Sept. 18 two policemen were shot dead also by anonymous gunmen in Dammam. They were killed while their patrol was attacked.

The police announced in August the arrest of a Yemeni suspected to kill a policeman in Bisha in southwestern Saudi Arabia. The suspect confessed to being a member of Islamic State (IS) militant group.

The IS sleeping cells have been involved in various terrorist attacks and blasts in the recent years.

Besides militant groups, the country's Eastern Province has witnessed disturbances by Shiite minority who are demanding more rights in the Sunni conservative state.