Millions of Shiites flooded the Iraqi shrine city of Karbala on Sunday for the peak of Ashura rituals, which have been largely spared the deadly attacks that struck pilgrims in past years.

Throngs of pilgrims beat their chests and some used swords to make cuts on their heads as a sign of mourning for Imam Hussein, grandson of the Prophet Mohammed who was killed in 680 AD by the armies of the caliph Yazid.

Tradition holds that the revered imam was decapitated and his body mutilated. Hussein's body is buried in the holy city, 100 kilometres (60 miles) south of Baghdad, and his death has become a formative event in Shiite Islam.

A man told black-clad pilgrims, many of them in tears, the story of the battle in which Hussein was killed, over loudspeakers near the shrine where he is buried.

Pilgrims later carried out a ritual run to the shrine, striking their heads in mourning and shouting: "We sacrifice for you, O Hussein."

Karbala provincial governor Amal al-Din al-Har said that about three million pilgrims, including 200,000 from foreign countries, have come to Karbala for the rituals.

Staff Lieutenant General Othman al-Ghanimi, head of Al-Furat al-Awsat operations command which covers Karbala, said 30,000 security forces personnel were deployed at the northern, southern and eastern entrances of the city to protect the pilgrims.

Lieutenant Colonel Ahmed Mohammed al-Hasnawi, the command's spokesman, meanwhile said its forces were also preparing to protect pilgrims on their way back to their homes.

Pilgrims are most vulnerable when they are going to and from Karbala, when they are not protected by the heavy security in the city itself.

He said that there will be 2,400 vehicles from various Iraqi ministries and from Karbala province to help transport pilgrims home.

There have not been any attacks on pilgrims in Karbala province so far, Hasnawi said.

Ahmed Fadhel, a 30-year-old pilgrim from Najaf province, said that both security and services in Karbala were good, but added: "We are ready to participate in this commemoration in spite of any circumstances."

This is the third year since the 2003 US-led invasion that Iraqi security forces have been in sole charge of security during Ashura.

Pilgrims were often targeted by bombings in past years that left dozens dead, including a wave of attacks against pilgrims the day before the peak of Ashura rituals last year that killed 28 people and wounded 78.

A car bomb against Shiite pilgrims north of Baghdad on November 17 this year killed three people and wounded 25, but pilgrims have largely been spared attacks.

Violence in Iraq is down significantly from its peak in 2006-2007, although bombings and shootings remain common, and Iraq's Shiite majority is frequently targeted by Sunni militants opposed to the Shiite-led government in Baghdad.

Attacks have hit Ashura commemorations elsewhere in the Muslim world this year.

In Pakistan, a bomb attack on a Shiite procession killed five people and wounded 83 on Sunday, while a similar attack the day before left eight people dead and a suicide bombing earlier in the week killed 23 people.

And in Yemen, gunmen shot dead three Shiites and wounded 10 on Saturday.

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.