Islamic State (IS) has claimed responsibility for a suicide bombing at a Shiite mosque in Saudi Arabia, warning that more "black days" loom ahead in a direct challenge to the rulers of the Sunni kingdom.

Yesterday's attack was the kingdom's deadliest militant assault since a 2004 al-Qaida attack on foreign worker compounds which sparked a massive Saudi security force crackdown.

However, this IS attack in the village of al-Qudeeh in the eastern Qatif region targeted Shiites, whom ultra-conservatives in Saudi Arabia regularly denounce as heretics.

The mosque attack killed at least 21 people and wounded 81, the official Saudi Press Agency reported.

A statement on the IS group's al-Bayan radio station, read aloud last night and posted this morning to militant websites associated with the extremists, identified the suicide bomber as a Saudi citizen with the nom de guerre Abu Amer al-Najdi.

The station also identified the attack as being carried out by a new IS branch in "Najd Province", referring to the historic region of the central Arabian Peninsula home to the Saudi capital, Riyadh.

IS - formerly al-Qaida's branch in Iraq which broke away and overran much of that country and neighboUring Syria - has become notorious for its attacks on Shiites, including a deadly Shiite mosque bombing in the Yemeni capital, Sanaa, that killed more than 130 people.

It was blamed for the killing of eight Shiites in a mosque shooting in eastern Saudi Arabia in November.

The al-Bayan message warned Shiites of coming "black days that will hurt you," pledging to expel all Shiites from the Arabian Peninsula.

The attack comes as Saudi Arabia is part of a US-led coalition targeting the IS group.

In late April, Saudi officials arrested 93 people they said were involved in an IS plot to attack the US Embassy and other targets.