Five people died when a gunman opened fire at a Shia prayer hall in Saudi Arabia in an attack claimed to be by Isis.
The gunman was shot dead by police, according to Al Arabiya TV, in a gun battle in Saihat that left nine other people injured.
Saudi Arabia's Interior Ministry said in a statement that the five dead included a woman but declined to comment on the likely motives or the identity of the gunman.
State television in Saudi Arabia reported that the gunman was wearing an explosives' belt and opened fire as the congregation in the hall was taking part in evening worship.
A previously unheard of branch of Isis, the extreme Sunni group which regards Shia Muslims as apostates, later posted a statement online in which it claimed responsibility for the slaughter.
The group called itself "Bahrain Province" and named the gunman as Shuja al-Dosari. It said he used a Kalashnikov rifle to attack worshippers as "they finished their polytheist rituals".
It is the third IS branch to appear in the Arabian Peninsula this year. Two other branches in Saudi Arabia have claimed responsibility for previous attacks on Shiites and security forces that killed nearly 70 people. The last attack before Friday's was in August when a suicide bomber hit a mosque inside a police compound in western Saudi Arabia and killed 15 people.
The name of the so-called Bahrain Province branch of the IS appears to be in reference to the historic area of Bahrain, which once encompassed the current island-state and parts of what is now the oil-rich eastern region of Saudi Arabia. The kingdom's eastern region and Bahrain are predominantly Shiite, though Saudi Arabia is majority Sunni and Bahrain's rulers are Sunni.
Friday's shooting took place in the city of Saihat, which is located in Saudi Arabia's al-Qatif region. Shiites traditionally pray at night in the lead up to Ashura, which falls this year on Oct. 24 in which many Shiite Muslims commemorate the martyrdom of the Prophet Muhammad's grandson through acts of self-flagellation.
The shooting came two days after the start of the Ashura commemorations, among the holiest dates in the calendar for Shia Muslims. During Ashura last year seven people, some of them children, were killed by gunmen in the town of al-Dalwa.