Authorities said on Thursday they had captured 73 suspected militants plotting to create violent "chaos" in Karbala, which is a frequent target of insurgents during Shiite Islam's most revered mourning ritual.
"Everything has gone well; everything has been secure," said Major Alaa Abbas, spokesman for Karbala police, noting that no security incidents had taken place in the city during the 10-day Ashura rituals.
He added: "Our security measures are still in place and our forces are still ready to prevent any attacks. They are still on alert."
Authorities said the 73 people arrested were Al-Qaeda-linked suspects implicated in plotting attacks against pilgrims in Karbala.
The arrests underscored fears of violence during the rituals, with heavy security on display throughout the commemorations.
Vehicle traffic in Karbala was at a virtual standstill as pilgrims were made to walk to the shrines, and all visitors were searched at checkpoints.
"If they had been able to mount their attacks during the pilgrimage, it would have created chaos," said Mohammed al-Mussawi, head of Karbala provincial council. "Karbala is the main target for terrorists during Ashura."
Mussawi said the number of pilgrims in Karbala for the commemorations had reached two million, 238,000 of them from abroad.
Some 28,000 soldiers and police are currently securing Karbala, with another 7,000 on stand-by, according to the army. They will remain in place for the coming days to ensure security as pilgrims return home.
This year marks the first time Iraqi troops have been in sole charge of security for Ashura. While the Americans have not provided ground forces for it in several years, they did help with surveillance and reconnaissance.
There are around 50,000 US troops still stationed in Iraq, but all of them must pull out of the country by the end of 2011, under the terms of a security pact.
Captain Dan Churchill, a US spokesman, said "the Iraqi security forces continue to demonstrate that they can successfully plan and operate for important large-scale security operations and are doing so for this year's Ashura and Arbaeen observances."
In previous years, Ashura has been a target for Sunni Arab extremists, who see the ceremonies as symbolically highlighting the split between Islam's two main branches.
This year, a total of 18 pilgrims were killed since the rituals began on December 8, police said, though none were in Karbala.
The ceremonies ended on Friday with a re-enactment of the Battle of Karbala in which Hussein was killed.
Masses of pilgrims symbolically rushed to the martyred saint's aid by taking part in a ritual five-kilometre (three-mile) run to Hussein's shrine, as they smacked their heads and screamed "Labeikeh Hussein" (Here we are, Hussein).
Then they re-enacted the scene of the final battle between Hussein and Yazid's armies, setting fire to tents set up for the occasion.
Tradition holds that the revered imam was decapitated and his body mutilated.
Earlier, mourners demonstrated their ritual guilt and remorse at not defending Hussein by cutting their scalps and flaying themselves with chains during processions.
Mournful songs blared from loudspeakers throughout the city and black flags were on display along with pictures of Hussein and his half-brother Imam Abbas, both of whom are buried in Karbala.
Now-executed dictator Saddam Hussein's Sunni-dominated regime barred the vast majority of Ashura commemorations throughout his rule until his overthrow in the US-led invasion of 2003.
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.
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