A suicide bomber blew himself up at a Shia mosque in eastern Saudi Arabia during Friday prayers, residents said, killing and wounding several people.
The interior ministry said the explosion hit the Imam Ali mosque in the village of Al Qadeeh in the Shia-majority Qatif region.
An interior ministry spokesman said an investigation has been opened and more details of the explosion would follow.
Estimating at least 30 casualties in the attack, where more than 150 people were praying.
However, an activist told Media that at least four worshippers were killed and others wounded. “We were doing the first part of the prayers when we heard the blast,” Kamal Jaafar Hassan, one worshipper, told Media by telephone from the scene.
The Saudi state news agency confirmed an explosion had occurred at a Shia mosque in eastern Saudi Arabia.
Pictures posted on social media showed bloodied victims being taken away on stretchers. An activist said 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.
Saudi police have made a string of arrests in recent months of Sunni extremists suspected of plotting attacks aimed at stirring sectarian unrest in confessionally divided Eastern Province.
Most of Saudi Arabia’s minority Shia live in the east, where they have long complained of marginalisation in the Sunni-dominated kingdom.
Last November, gunmen killed seven Shia, including children, in the eastern town of Al-Dalwa during the Ashura.
Four men carried out the attack after killing a man from a neighbouring village and stealing his car to use in the shootings, the interior ministry said.
Last month, the interior ministry said it had dismantled a 65-strong cell with suspected links to the Islamic State jihadist group in Iraq and Syria that was implicated in a plot to “incite sectarian sedition” through similar attacks.
Since 2011, protests and sporadic attacks on security forces have occurred in Shia-majority areas, leaving about 20 Shia youths dead.