Saudi Arabian security officials moved aggressively on Tuesday to crush an outbreak of anti-Shiite violence, arresting 15 people in six cities and killing two others in connection with what the Interior Ministry called a terrorist ambush on mosque worshipers in a minority Shiite community.
At least two security officers were killed and two wounded in the crackdown on the suspected mosque assailants, who were armed with pistols and machine guns, the Interior Ministry and government-run Saudi news media reported.
The mosque ambush, which occurred Monday night and left at least five people dead, came as Shiites, who are a small minority in heavily Sunni Saudi Arabia, were celebrating the eve of Ashura, one of the most sacred holidays in the Shiite branch of Islam.
The identities of the assailants and their affiliations were not disclosed. But the ambush raised speculation that Saudi-born Sunni jihadists who had joined Islamic militant groups in Iraq and Syria had brought their violent zealotry home, an outcome that Saudi rulers have long feared.
Earlier this year King Abdullah issued a decree that reinforced existing counterterrorism laws and warned that “membership in terrorist organizations and participation in hostilities outside the kingdom will not be tolerated.”
The mosque assault risked aggravating Shiite frictions with Sunnis not only in Saudi Arabia but elsewhere in the Middle East, where tensions between the two branches are a theme in conflicts convulsing the region.
Shiite worshipers in neighboring Iraq have often been attacked by Sunnis during the Ashura holiday, with the risks considered even greater this year because of the rise of the Islamic State, the extremist Sunni militant group that considers Shiites to be heretics deserving of death.
Somewhat incongruously, however, hundreds of thousands of Shiite pilgrims celebrated the holiday in Iraq on Tuesday without any significant attacks by Sunni extremists, according to press accounts from the region.