Two million Shiites geared up for the climax of Ashura commemorations in the Iraqi shrine city of Karbala on Friday, the day after authorities said they arrested dozens of suspected militants plotting "chaos."
The rituals, largely peaceful thus far and marking the killing of Imam Hussein by armies of the caliph Yazid in 680 AD, are a key test for Iraqi forces ahead of a complete withdrawal of American troops in a year.
The 10-day ceremonies in the holy city south of Baghdad began with pilgrims drenched in blood after ritually slicing their scalps and self-flagellation in a demonstration of mourning, and were ending Friday with a re-enactment of the battle of Karbala in which Hussein was killed.
Masses of black-clad pilgrims were to symbolically rush to the martyred saint's aid by taking part in a ritual five-kilometre (three-mile) run to Hussein's shrine, as they smack their heads and scream "Labeikeh Hussein" (here we are, Hussein).
Then they re-enact 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.
On Thursday, Iraqi authorities said they had arrested 73 Al-Qaeda-linked suspects who officials said were implicated in plotting attacks against pilgrims in Karbala.
The arrests underscored fears of violence during the 10-day 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, as all visitors were searched at checkpoints.
"We were able to destroy 14 terrorist cells and arrest 73 people, including 37 wanted persons," Karbala provincial council chief Mohammed al-Mussawi told AFP. "We seized lots of weapons, IEDs (improvised explosive devices), explosives belts and equipment.
"If they had been able to mount their attacks during the pilgrimage, it would have created chaos. Karbala is the main target for terrorists during Ashura."
Mussawi said those arrested were suspected members of Al-Qaeda.
He said the number of pilgrims in Karbala for the commemorations had reached two million, 238,000 of them from abroad.
Around 28,000 soldiers and police are currently securing Karbala, with another 7,000 available if needed, according to the army.
This year marks the first time Iraqi troops have been in sole charge of security for Ashura. While American troops have not provided ground forces for Ashura in several years, they had helped with surveillance and reconnaissance.
In previous years, Ashura has been a target for Sunni Arab extremists, who see the 10-day ceremonies as symbolically highlighting the split between Islam's two main branches.
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.