Iraqi authorities arrested 80 people suspected of plotting attacks in the southern city of Karbala, where authorities said as many as 2 million pilgrims were gathering for the Shiite Muslim ceremonies of Ashura.

The suspects are from the Boys of Heaven, a Sunni Muslim militant group with links to al-Qaeda and the banned Baath party of ousted President Saddam Hussein, General Othman al-Ghanimi said at a Baghdad news conference late yesterday.

The pilgrims are gathering for the climax of 10 days of rituals honoring Hussein Ibn Ali, the third Shiite imam. Ashura is observed annually by Shiites in countries including neighboring Iran and Lebanon as well as in Pakistan. Karbala is where the imam, a grandson of the Prophet Muhammad, was killed in battle in the seventh century and is buried.

Sunni militants have previously carried out attacks during Ashura in an attempt to ignite tensions between Sunnis and Shiites. The deadliest such attacks in Iraq were in March 2004, when 170 people were killed in bombings at Shiite mosques in Baghdad and Karbala.

Security has been boosted for the ceremonies this year, with about 28,000 soldiers and police deployed in Karbala and another 7,000 on standby to protect the pilgrims, al-Ghanimi said. About 100,000 foreigners are among the 2 million who are attending, he said.

Iraqi authorities have announced a number of arrests in recent weeks. Interior Minister Jawad al-Bolani said on Nov. 27 that Iraq’s security forces had captured 12 suspected militants, and on Dec. 2 he announced the arrest of 39 more.

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