A Saudi citizen suspected of organizing the attack on Shiite worshipers in the oil-rich Eastern Province returned from fighting in Iraq and Syria, according to Saudi-owned newspapers.

The citizen organized a cell that carried out the attack that killed seven people in the Shiite village of al-Dalwah after sneaking across the border into the kingdom, al-Hayat and Saudi Gazette newspapers said, citing security officials they didn’t identify. Asharq Al-Awsat said the Saudi fought in regional conflicts. The Interior Ministry declined to comment, citing the ongoing investigation.

This would be the first time that a Saudi returning from the latest conflicts in Iraq and Syria attacked targets in the world’s largest oil exporter, raising concern that sectarian violence may escalate. Saudi Arabia is participating in a U.S.- led military campaign against Islamic State, the al-Qaeda breakaway group that has seized large parts of Syria and Iraq and used social media to recruit Saudi men.

“The Saudis have good reason to be concerned, and the indications are that Saudi authorities are indeed concerned,” said Paul Pillar, a former intelligence officer for the Near East and South Asia at the Central Intelligence Agency. “This attack may herald other forms of violence within Saudi Arabia perpetrated by jihadists who had fought in Syria, Iraq, or elsewhere and are now returning home.”

Arrest Raids

The leader of the cell was injured and arrested in clashes with security forces, al-Hayat reported. The cell included 22 members, 11 of whom had been imprisoned by Saudi authorities for “security” reasons, the London-based newspaper said.

Saudi authorities called the Nov. 3 shooting of the Shiites in the village a terrorist attack. Police detained 15 people and killed three suspects in raids across six cities, the official Saudi Press Agency reported. Two security personnel were killed during a raid in Buraidah in the central Qassim region, according to the news service.

The strike in the al-Ahsa oasis occurred at a ceremonial hall known as a Husseiniya during the Shiite religious celebration of Ashoura. Senior Sunni and Shiite religious scholars quickly condemned the attack as they seek to prevent sectarian tension in the Arab world’s biggest economy.

The kingdom’s Interior Minister Mohammed bin Nayef visited the families of the victims and the injured in al-Ahsa, where he conveyed King Abdullah’s condolences, the Saudi Press Agency reported. Sheikh Abdulaziz Al-Asheikh, the kingdom’s most senior Islamic scholar, said “sick minds” carried out this “brutal aggression.”

If such attacks continue, “this is a very interesting tactic by the regime’s opponents,” said Gregory Gause, head of the International Affairs Department at Texas A&M University. “Target the Shiite, force the state to defend the Shiite and try to polarize more Sunni opinion against the state. I do not think it will work, but it is worth following.”