DUBAI: A suicide bomber killed 21 people on Friday in a packed mosque in eastern Saudi Arabia, residents and the health minister said, the first attack in the kingdom to be claimed by militants of the self-styled Islamic State (IS).

It was one of the deadliest attacks in recent years in the largest Gulf Arab country.

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

A video clip 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 completing the first part of the prayers when we heard the blast,` Kamal Jaafar Hassan said by phone from the scene.

In a statement, IS said that one of its suicide bombers, identified as Abu Ammar alNajdi, carried out the attackusing an explosives-laden belt that killed or wounded 250 people, US-based monitoring group SITE said on its Twitter account.

IS said it would not rest until Shias were driven from the Arabian peninsula.

Saudi officials have said the group is trying hard to attack the kingdom, which is an important ally for Western countries battling IS and a symbolic target for the jihadist group itself.

In November the Sunni group`s leader, Abu Bakr alBaghdadi, called for attacks against the rulers of Saudi Arabia, which has declared IS a terrorist organisation, joined international air strikes against it, and mobilised top clergy to denounce it.

Last week Baghdadi delivered another speech laden with derogatory comments about the Saudi leadership and the country`s Shia minority.

Friday`s bombing was the first attack targeting Shias since November, when gunmen opened fire during a religious celebration in alAhsa, also in the east.

The Interior Ministry described the attack as an act of terrorism and said it was carried out by `agents of sedition trying to target the kingdom`s national fabric`, according to a statement carried by state news agency SPA.

The agency quoted an Interior Ministry spokesman as saying the bomber detonated a suicide belt hidden under his clothes inside the mosque.

`Security authorities will spare no efforts in the pursuit of all those involved in this terrorist crime,` the of ficial saidin a statement carried by SPA.

A hospital of ficial said by telephone that `around 20 people` were killed in the attack and more than 50 were being treated, some of them suffering from serious injuries. He said a number of other people had been treated and sent home.

In April, Saudi Arabia said it was on high alert for possible attacks on oil installations or shopping malls.-Reuters