At least 21 worshippers were killed in a suicide blast that targeted a Shia mosque in eastern Saudi Arabia on Friday, media reported.
The explosion that targeted Imam Ali Mosque in Qudaih area of the Saudi city of Qatif also left 66 Shia worshipers injured, Xinhua news agency reported citing Al Arabiya News.
As many as 150 Shia worshippers were inside the mosque when the blast took place, Xinhua news agency reported citing Al Arabiya News.
Several Twitter accounts of the Islamic State (IS) claimed responsibility for the blast.
An interior ministry spokesman said an investigation has been launched into the incident and that more details will follow.
Last November, three masked gunmen killed five Shias and injured nine others in the eastern town of Aldaloh in Ahsa governorate.
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Saudi authorities arrested six suspects in connection with November's attack.
Most of Saudi Arabia's minority Shias live in the eastern region, where they have long protested against marginalisation in the Sunni-dominated kingdom.
Saudi security authorities have been involved in a war against internal terror and extremism. Terror cells linked to the IS have been recently dismantled.