Iraqi Shi'ite worshippers beat drums as they mark Ashura in Baghdad, Iraq, Tuesday, Jan. 6, 2009.

Thousands of Shi'ites gathered in the central Iraqi city of Karbala Tuesday, to mark the start of the annual religious observance of Ashura.

Men and boys marched down the streets of Karbala with blood streaming down their faces after cutting their scalps, part of the self-flagellation that accompanies some Ashura rituals.  Many pilgrims came from Iran, a majority Shi'ite nation.

Iraqi military officials say some 20,000 security forces have deployed throughout the city to protect worshippers. 

Ashura is one of the most important holy days for Shi'ites.  It marks the death in battle more than 13-hundred years ago of Imam Hussein, grandson of the Prophet Muhammad.

On Monday, a U.S. commander in Iraq's heavily Shi'ite region south of Baghdad said troops are on alert for female suicide bombers during Ashura.

Colonel Butch Kievenaar said he has information that al-Qaida may send female suicide bombers to disrupt the religious observance.

On Sunday, a suicide blast in northern Baghdad killed at least 35 people and wounded 72 others.  Authorities originally said the bomber was a woman, but Iraqi officials now say the bomber was a man disguised in women's clothing.

In other news, Iraqi police say gunmen on Monday killed a member of Iraqi President Jalal Talabani's political party in a drive-by shooting in the northern city of Kirkuk.

Authorities say the official killed, Subhi Hassan, belonged to Mr. Talabani's Kurdish party, the Patriotic Union of Kurdistan.