A suicide bomber killed 21 worshipers during Friday prayers in a packed Shia mosque in eastern Saudi Arabia, residents and the health minister said, in an attack claimed by the Islamic State militant group.

It was one of the deadliest assaults in recent years in the kingdom, where sectarian tensions have been frayed by nearly two months of Saudi-led air strikes on Shia Houthi rebels in neighboring Yemen.

More than 150 people were praying when the huge explosion ripped through the Imam Ali mosque in the village of al-Qadeeh, witnesses said.

A video posted online showed a hall filled with smoke and dust, with bloodied people moaning with pain as they lay on the floor littered with concrete and glass. More than 90 people were wounded, the Saudi health minister told state television.

"We were doing the first part of the prayers when we heard the blast," worshipper Kamal Jaafar Hassan told Reuters by phone from the scene.

It was the first attack targeting minority Shias since November when gunmen opened fire during a religious celebration in al-Ahsa, also in the east where most of the group live in predominantly Sunni Muslim Saudi Arabia.

Islamic State said in a statement that one of its suicide bombers identified as Abu 'Ammar al-Najdi carried out the attack using an explosives-laden belt that killed or wounded 250 people, US-based monitoring group SITE said on its Twitter account.