Security forces have beefed up their presence in Karbala and authorities are also checking on the 60,000-odd foreign worshippers expected to attend the ceremonies to ensure they do not have swine flu.
Black flags, representing the sadness of Shiites during Ashura, were seen all over the central Iraqi city, south of Baghdad, along with pictures of Imam Hussein and Imam Abbas, who are both buried here.
Masses of pilgrims, most of them dressed in black, gathered around the Imam Hussein shrine in Karbala's Old City on Saturday evening.
The 10-day Ashura rituals which end on Sunday commemorate the killing of Imam Hussein, a grandson of the Prophet Mohammed, by armies of the Sunni caliph Yazid in 680.
"I came to show my belief in Imam Hussein -- this event has nothing to do with personal motivations or politics," said 40-year-old Mohammed Abdul Hussein, who travelled from neighbouring Babil province.
Karbala police chief General Ali Jassim Mohammed said that around 25,000 policemen and soldiers had been deployed to secure the commemoration ceremonies.
Security perimeters have also been formed throughout the city, while helicopters are providing extra surveillance and bomb-sniffing dogs are being used at checkpoints.
To counter women suicide attackers who have struck Karbala before, security forces have deployed 600 female personnel on three roads into the city. Cameras are also monitoring pilgrims' movements across Karbala.
During Ashura in March 2004, near-simultaneous bombings at a Shiite mosque in Baghdad and in Karbala killed more than 170 people.
Since Tuesday, 28 people have been killed and more than 130 wounded in violence targeting Ashura, including attacks on worshippers in Karbala and Baghdad.
Saturday afternoon, a blast targeting a procession marking Ashura in Baghdad Jadida (new Baghdad) in the east of the capital killed two people and wounded eight others.
And in the Shiite district of Abu Tcheer, south Baghdad, an explosion against a procession killed one person and wounded nine others.
A roadside bomb also killed six people, most them children on Friday in the predominantly Shiite Baghdad neighbourhood of Sadr City. Twenty-six others were wounded in the attack that struck an Ashura procession.
A day earlier in Karbala, a bomb killed one person and wounded 12.
Security chiefs have also vowed to prevent any political exploitation of the festival as Iraq prepares to go to the polls for parliamentary elections on March 7.
Authorities are also concerned about the spread of swine flu from foreign worshippers, the majority of whom are arriving from Iran, Pakistan and Arab Gulf countries.
"We expect more than 60,000 foreign pilgrims to come, and we have ordered them to visit health centres to be sure they do not have any diseases," said provincial governor Amal Adin al-Her.
"All hotel owners must inform authorities about any cases of illness among their residents."
He estimates that 1.5 million pilgrims will visit Karbala on Saturday and Sunday.
Ashura, which means tenth in Arabic, falls on the 10th day of the Muslim month of Muharram.
Tradition holds that Hussein, a grandson of the Prophet Mohammed, was decapitated and his body mutilated by the armies of the caliph Yazid.
To express remorse and guilt for not saving Hussein, Shiite volunteers flay themselves with chains or slice their scalps during processions to the Karbala shrines.
Shiites make up around 15 percent of Muslims worldwide. They represent the majority populations in Iraq, Iran and Bahrain and form significant communities in Afghanistan, Lebanon, Pakistan and Saudi Arabia.
Six other people were also killed in separate attacks Saturday, including a Sunni Muslim tribal leader who died in a bomb explosion in Abu Ghreib just west of the capital, and the wife of a traffic policeman killed in a drive-by shooting in west Baghdad.
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