A witness says gunfire has struck a Shiite mosque in eastern Saudi Arabia, wounding a number of people.

Mohammed al-Nimr told The Associated Press the attack struck the mosque during Friday prayers. Al-Nimr said security forces and ambulances quickly surrounded the mosque.

Saudi state media did not immediately report on the attack.

Shiites in Saudi Arabia previously have been targeted in attacks by the Islamic State group in the kingdom. 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.

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Associated Press writer Reem Khalifa in Manama, Bahrain, contributed to this report.