A suicide attack on a Shiite mosque in the east of Saudi Arabia during Friday prayers has killed around 20 people, a hospital official says. The Islamic State has reportedly claimed responsibility for the attack.

The official told Reuters that more than 50 people had been wounded after the suicide bomber let off his device.

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

The blast occurred at the Iman Ali mosque in the town of al-Qadeeh, Qatif province, where around 150 people were praying.

The Islamic State (IS, formerly ISIS/ISIL) has claimed responsibility for the attack, US-based monitoring group SITE said on its Twitter account. The militant group reportedlyidentified the suicide bomber as Abu 'Ammar al-Najdi, stating that the assault was carried out using an explosives-laden belt.

Photographs from the scene show bodies strewn across the ground, and emergency vehicles at the scene. Inside the mosque, glass has been shattered; pieces of concrete, perhaps from the ceiling, are littered across the floor.

Another photograph showed the mutilated body of a young man, who was believed to have been the suicide bomber.

The Saudi Interior Ministry described the attack as an act of terrorism, saying 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.

"Security authorities will spare no effort in the pursuit of all those involved in this terrorist crime," a ministry official said.

WARNING: You may find the pictures below disturbing

#تفجير_حسينية_الرافضة shia masjid been targeted in saudi Arabia 22 dead till now Allah Akbar Wa Alhamduliah pic.twitter.com/clz3YSG8R1 — 31spɹoʍsɟoɯɹoʇs (@StormOfSwords13) May 22, 2015

The attack is the first to target Shiite Muslims in Saudi Arabia since November, when a gunman killed at least eight people in an attack on a religious celebration, which was also in the east of the kingdom.

BREAKING: Photos coming in from the terrorist attack on Shiite mosque in Qatif, Saudi Arabia. Over 10 people killed. pic.twitter.com/5QXIT4krrE — Ibrahim Halawi (@Ibrahimhalawi) May 22, 2015

Catherine Shakdam, from the Beirut Centre for Middle East studies, told RT she believes radical Sunni groups are likely responsible for the suicide bombing.

“Bearing in mind that it happened in Qatif, which is an Eastern region of Saudi Arabia and has a Shiite Muslim majority, we think that a Wahhabi group or ISIS, which is basically the same thing, may be responsible,” said Shakdam.

“This is very much in keeping with the narrative coming out of the Kingdom recently, when it comes to the sectarian hatred that they have committed,” she added.

أنباء عن سقوط 6 ضحايا وعشرات الجرحى في تفجير انتحاري استهدف مصلين في جامع الامام علي - القديح- القطيف #السعوديةpic.twitter.com/IzGVfexVjz — Marwan Matni (@marwanmatni) May 22, 2015

The al-Qadeeh town is home to Saudi Arabia’s Shiite minority, in a country which is predominantly Sunni.

Shiites make up around 10-15 percent of the Saudi Arabian population. They are mainly based in two districts in the Eastern province, not far from Bahrain, in Qatif and al-Ahsa.