Saudi Arabia has confirmed that Friday's suicide bombing at a Shiite mosque in the east of the country that killed 21 was carried out by an Islamic State militant, backing up an earlier claim by the group.

The Interior Ministry identified the bomber as Saudi citizen Saleh bin Abdulrahman al-Qashaami in a statement carried by the official Saudi Press Agency late Saturday.

Al-Qashaami was wanted for being an active member of an IS-linked terrorist cell, the ministry said. Lab tests showed that the explosive use in the bombing was a military-grade compound known as RDX.

The attack in the village of al-Qudeeh in the eastern Qatif region was the deadliest assault by militants in the kingdom since a 2004 al-Qaida attack on foreign worker compounds.

It targeted members of Saudi Arabia's Shiite minority - a sect that both the Islamic State group and ultraconservatives in Saudi Arabia regularly denounce as heretics.

A statement from the IS group's al-Bayan radio station posted to militant websites Saturday said a new branch of the group was behind the attack, which it said was carried out by a Saudi going by the nom de guerre Abu Amer al-Najdi.

The IS group's activities are primarily focused on Iraq and Syria. Its claim of responsibility for Friday's strike and the official Saudi confirmation bolster concerns it has established a toehold inside the oil-rich kingdom, as it has done in Libya and Egypt's Sinai Peninsula.

It has warned of more "black days" for Shiites in Saudi Arabia, a member of the U.S.-led coalition targeting the group.

The Saudi Interior Ministry said the group also was responsible for the shooting death of a police officer in Riyadh earlier this month. It said five members of an IS cell killed Pvt. Majed Ayedh al-Ghamdi and burned his body. Authorities recovered guns, ammunition, explosives and other items from a farm linked to the militants, it said.