A suicide bomber has set off an explosion during weekly prayers at a Shia mosque in eastern Saudi Arabia leaving at least 19 dead, the interior ministry spokesman said in a statement.

“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 spokesman called the attack an act of terrorism, vowing that “Security authorities will spare no effort in the pursuit of all those involved in this terrorist crime”.

Al Jazeera’s Hashem Ahelbarra, reporting from the capital Riyadh, said authorities expected the death toll the 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.

Saudi Arabia’s Shia population is mostly based in two oasis districts of the Eastern Province, Qatif on the Gulf coast, and al-Ahsa, southwest of the provincial capital al-Khobar.

The community accounts for between 10 to 15 percent of the total population.

No one immediately claimed responsibility for the bombing, the first to target the Shia community in Saudi Arabia since November when gunmen killed at least eight people in an attack on a religious anniversary celebration, also in the east. Al Jazeera