Riyadh: Many people were killed Friday when a suicide bomber attacked weekly prayers in a Shia mosque in eastern Saudi Arabia.

“It has been established that an individual detonated a bomb he was wearing under his clothes during Friday prayers at Ali Ibn Abi Taleb mosque in Kudeih in Qatif province,” the interior ministry spokesman said.

A statement carried by the official SPA news agency quoted the spokesperson as saying that the attack left many dead and wounded.

An activist said at least four worshippers were killed and others wounded.

Qatif hospital issued an urgent call for blood donations after the attack and called in off-duty staff to cope with the high number of casualties, the activist said.

The government has ordered a probe, the telegraph.uk reported.

Saudi police have made a string of arrests in recent months of Sunni extremists suspected of plotting attacks aimed at stirring sectarian unrest in eastern province.

Most of Saudi Arabia’s minority Shias live in the east, where they have long complained of marginalization in the Sunni-dominated kingdom.