Violent clashes broke out between residents of the Saudi holy city of Medina on the day minority Shiite Muslims commemorated the death of their most sacred saint, a security official said on Saturday.

The official refused to elaborate on the cause of Thursday’s clashes, but a Shiite news website called Rasid reported that hundreds of Sunni hard-liners attacked those participating in the commemorations, known as Ashoura. The day of mourning marks the killing of the Prophet Muhammad’s grandson Hussein in the year 680 in present day Iraq.

The slaying of Hussein is a defining moment in the history of Islam and helped seal the split between the faith’s two main sects, Sunnism and Shiism. In recent years, attacks by Sunni extremists have marred Ashoura commemorations in Iraq, Pakistan and other places of strife.

Shiites are 10 percent of predominantly Sunni Saudi Arabia’s 22.6 million people. They complain of discrimination, saying they are barred from key positions in the military and government and are not given an equal share of the country’s wealth.

During Thursday’s clashes, security forces were deployed to disperse the crowds, the security official said, speaking on condition of anonymity because he was not authorized to speak to the press.

The Rasid website said residents of Medina’s Asbaa neighborhood, which is mostly Sunni, used poles and stones in their assault against Shiites in the nearby Qabaa district, home to a number of Shiite places of worship.

Several Saudi newspapers reported the violence, but for the most part without mentioning any sectarian element.

Though one paper, Al-Riyadh, blamed “young zealots who were wearing black clothes,” in a reference to Shiites participating in the mourning rituals.

The Saudi Medina daily said 38 people were arrested, three policemen were injured and 36 cars were damaged.

The Al-Watan daily said security forces fired gunshots in the air after failing for two hours to end the clashes.

Sunni distrust of Shiites is both religious and political. The hard-line Wahhabi school of Islam, which is the state religion in Saudi Arabia, considers Shiites infidels.

The government is thought to fear that Saudi Shiites will be emboldened by the increased power of Shiites in Iraq since the 2003 fall of Saddam Hussein. They also are concerned that Shiite power Iran will use fellow Shiites to destabilize the kingdom.

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