A shooting at a Shiite mosque in eastern Saudi Arabia killed three people and wounded others Friday during prayers, security officials and a witness said, in the latest violence to strike the region.

The attack struck the Imam Reza Mosque in the neighborhood of Mehasin, an area popular with Shiite workers of the state-run Saudi Arabian Oil Co., the world’s largest oil producing firm. Images on social media showed wounded laying on the mosque’s floor.

The security officials said the three dead was an initial toll. They spoke on condition of anonymity as a formal announcement had yet to be made.

Witness Mohammed al-Nimr told The Associated Press that security forces and ambulances quickly surrounded the mosque. He said that it was a shooting and that worshippers stopped the attacker from detonating a suicide bomb belt.

Saudi state media did not immediately report on the incident. In the attack’s chaotic aftermath, Saudi police fired assault rifles into the air to drive away an angry mob that surrounded a police car holding the suspected attacker, according to video shot from the scene.

Shiites in Saudi Arabia make up some 10 to 15 per cent of the ultra-conservative, Sunni-ruled kingdom’s population. The minority group, many of whom live in the country’s oil-producing east, previously have been targeted in attacks by the Islamic State group, which views Shiites as heretics. No group immediately claimed Friday’s attack.

Earlier this month, Saudi officials also executed a prominent Shiite cleric from the region, raising tensions in the area.

Al-Nimr is the brother of the executed cleric, Sheikh Nimr al-Nimr.