A suicide bomber blew himself up at a mosque in Najran in southern Saudi Arabia on Monday, killing at least three people and wounding several others, Saudi-owned al-Arabiya television reported.
Militant group Islamic State claimed responsibility for the attack a few hours later.
The operation targeted "the rejectionist Ismailis" said a statement carried by the group posted on Twitter, referring to the Ismaili Shia sect who are a minority in Saudi Arabia, Reuters reported.
The attack on the al-Mashhad mosque occurred during evening prayers, and authorities were investigating the bombing, www.sabq.org, a Saudi news website, reported.
A video shared by daily newspaper al-Watan showed panicked worshippers fleeing the scene and a child falling to his knees as sirens wailed and dust filled the street.
On Aug. 6, a suicide bomber killed at least 15 people in an attack on a mosque used by members of a local security force in southwest Saudi Arabia, an assault that an online statement said was carried out by Islamic State.
In May, two suicide bomb attacks on Shi'ite Muslim mosques in Saudi Arabia were claimed by Islamic State. The first on a mosque in Qatif in the east of the kingdom killed 21 worshippers, and another four died in a bombing a week later at a mosque in Dammam.
Another bombing claimed by Islamic State on a Shia mosque in Kuwait in June killed 27 people.
The militant group, bitterly opposed to Gulf Arab rulers, is trying to stir sectarian confrontation on the Arabian peninsula to bring about the overthrow of the states' ruling dynasties. It has urged young Saudi Sunni Muslims in the kingdom to attack targets including Shia.