Saudi Arabia on Saturday confirmed the suicide bomber who killed 21 worshippers at a Shiite mosque had links with the Islamic State group, in what the interior ministry called an attempt to promote sectarian strife.
It was the deadliest attack in years to strike the Sunni-dominated kingdom, and marked the first time the jihadist IS group officially claimed an attack in Saudi Arabia.
"His name was Salih bin Abdulrahman Salih al-Ghishaami, a Saudi national," the interior ministry said in a statement carried by the official Saudi Press Agency.
"He was wanted by security services for belonging to a terrorist cell receiving directions from Daesh abroad," it said, using the Arabic acronym for IS.
The militant group had already claimed the attack on Friday in Eastern Province, but it identified the bomber as Abu Amer al-Najdi.
"The cell was discovered last month, and so far 26 of its members, all Saudi nationals, have been arrested," the interior ministry said, raising the number of wounded from 81 to 101.
The bomber struck during the main weekly prayers at a mosque in the Shiite-majority city of Qatif.
It is the second mass murder of Shiites in the kingdom since late last year, and locals in the city took to the streets Saturday to protest the attack.
In November gunmen killed seven Shiites including children in the Eastern Province town of Al-Dalwa.
At the time, authorities said the suspects were linked to IS.
Although Sunni extremists attacked Westerners and government targets in Saudi Arabia between 2003 and 2007, the Al-Dalwa shootings were the first major militant assault against Shiites.
The IS group, which considers Shiites heretics, has declared a "caliphate" in seized parts of Iraq and Syria. It has claimed numerous atrocities including the beheading of foreign hostages.
Saudi Arabia and its Sunni Gulf neighbours last year joined a US-led military coalition bombing IS in Syria, raising concerns about possible retaliation in the kingdom.
Since late March the kingdom has also led a coalition bombing Iran-backed Shiite rebels who seized large parts of Yemen and have sent deadly shell fire into Saudi Arabia.
In its statement claiming responsibility for the Qatif attack, IS vowed "dark days ahead" for Shiites until militants "chase them from the Arabian Peninsula".
Political and religious leaders in the kingdom, and its media, were unanimous in denouncing the mosque bombing.
"No room for discord... the people are united," said the Al-Watan daily.
The interior ministry said the attack against "honourable citizens was carried out by tools controlled by foreign forces that aim to divide the unity of society and pull it into sectarian strife".
But widespread condemnation by Saudi society "sends the message to them that their endeavours have failed," the ministry said.
Saudi Arabia's top cleric, Grand Mufti Sheikh Abdul Aziz al-Sheikh, called it a "criminal act" which targeted national unity.
The United Nations Security Council and Saudi Arabia's regional Shiite rival Iran condemned the mosque attack.
Most of the kingdom's Shiites live in the east, where the vast majority of the kingdom's oil reserves lie but where Shiites have long complained of marginalisation.
The Qatif attack occurred despite the arrest since December of nearly 100 jihadists, most of them allegedly linked to IS.
The interior ministry said five members of the suicide bomber's 26-member cell were involved in the May 8 shooting of a policeman on patrol in southern Riyadh.
"They had confessed to their crime and set fire to his body," the ministry said.
Investigators recovered two Kalashnikov rifles used in the policeman's murder, 17 other firearms, and 230 kilograms (507 pounds) of chemicals used for making explosives.
The other 21 detained suspects included two 15-year-olds and one who was 16, the ministry said.
It added that all 21 "had adopted the ideology of the terrorist Daesh," and recruited followers especially among young people.
Frederic Wehrey, a Gulf analyst at the US-based Carnegie Endowment for International Peace, has written that the kingdom's vows to counter the Islamic State group and its sectarianism expose a paradox.
"In its own domestic policies, the Saudi government has institutionalised sectarianism in virtually every aspect of political, social, and economic life," Wehrey wrote in a December article for Foreign Policy.