(Adds Interior Ministry, paragraph 5)

RIYADH, Aug 6 (Reuters) - Saudi Sunni Muslim religious police assaulted and detained a group of mainly Iraqi Shi'ite pilgrims to Islam's holy city of Mecca this month, Saudi and Iraqi sources said on Monday.

Tension is high in the region because of sectarian violence between Sunni and Shi'ite Muslims in Iraq, and many Saudis are among the foreign fighters with al Qaeda suspected of carrying out suicide bomb attacks against Iraq's majority Shi'ites.

Iraq's defeat of Saudi Arabia, which sees itself as the leader of Sunni Islam, in the final of the Asian Cup soccer competition has also provoked some anti-Shi'ite comments in Islamist Internet chatrooms.

A report on rasid.net, a key news source among Saudi Arabia's minority Shi'ite Muslims, said religious police surrounded a group of Iraqi pilgrims inside the Grand Mosque in Mecca on Sunday. They called them "infidels", then began hitting them, it said.

An Interior Ministry spokesman was not available for comment, and Mecca's mayor Osama al-Bar said he had no information about the case.

Officials say disputes sometimes break out in the summer heat as pilgrims crowd into Mecca.

The group, which included sons of Iraqi politicians and British and U.S. nationals, was held in detention for up to 24 hours and some needed medical treatment, the Web site said.

Iraqi parliamentarian Ridda Jawad al-Takki said the group, which included his son, had been singled out for being Shi'ite.

"They were beaten up because they were holding Shi'ite-style prayers," he said, adding his son has been admitted to hospital in Mecca.

Saudi Arabia practises a strict form of Sunni Islam and some clerics view Shi'ism as a heresy. Religious police, who often carry sticks, are charged with ensuring Sunni rites and beliefs dominate in the desert country.

Saudi Arabia hosts millions of pilgrims year-round in the holy cities of Mecca and in Medina, where religious police are more tolerant of Muslims of different backgrounds. (Additional reporting by Mariam Karouny in Baghdad)

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