Islamic State (Isis) has claimed responsibility for a suicide bombing in Saudi Arabia's eastern province that killed over 20 people while they prayed at a local mosque. The bombing marks the first time IS has struck inside Saudi Arabia.

The jihadi group has issued a statement in Arabic on Twitter as well as what appears to be a photograph of the bomber, who targeted a Shi'ite mosque in the village of al-Qadeeh.

The village is in the restive Shi'ite province of Qatif, which has seen rising tensions between Shi'ite residents and nearby Sunni tribes as well as with the Saudi Arabian government.

The statement is impossible to verify but both Syria-based monitoring group Raqqa is Being Slaughtered Silently and a number of other terrorist monitoring sites published it late on 22 May.

#ISIS claims responsibility for the suicide attack on a mosque in #SaudiArabia today pic.twitter.com/55uPsS9WHI May 22, 2015

Earlier, a suicide bomber targeted a mosque in Sana'a, the Yemini capital, in an attack also claimed by IS.

In Qatif, witnesses told Reuters the huge explosion took place at the Imam Ali mosque in the village of al-Qadeeh where 150 Muslims had gathered for Friday prayers.

Graphic images shared on social media showed victims covered in blood being taken away on stretchers. Other pictures showed shattered glass, debris next to the tiled pillars and bodies covered in sheets laid out on the floor.

The Saudi state news agency confirmed a blast had occurred at a mosque in eastern Saudi Arabia. A spokesman for the Saudi Interior Ministry said the bomber detonated a suicide belt hidden under his clothes inside the mosque causing several people to be "martyred or wounded".

In a statement carried by state news agency SPA, the official said: "Security authorities will spare no effort in the pursuit of all those involved in this terrorist crime."