RNA - the Saudi interior ministry said in a statement that a suicide bomber had set off an explosion during weekly prayers at a Shia mosque, leaving at least 19 dead.
"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 statement, which was carried by the official SPA news agency, said.
The figures were announced by Saudi Health Minister Khalid al-Faleh on Friday following the attack.
Later in the day, the Takfiri ISIL terrorist group claimed responsibility for the attack.
The statement issued by ISIL said "the soldiers of the Caliphate" were behind Friday's attack by a suicide bomber "who detonated an explosives belt" in the mosque in the Shia-majority city of Qatif.
Authorities expected the death toll to rise.
Pictures posted on social media purported to show the devastation, with dead bodies strewn across the floor and shattered glass covering the courtyard of the mosque.
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