By Ahmed Rasheed
BAGHDAD, Dec 24 (Reuters) - Hundreds of thousands of Shi'ite Muslims observed the holy day of Arbaeen in the Iraqi city of Kerbala on Tuesday under heavy security after a string of attacks killed scores of people over the past week.
Guarded by tens of thousands of Iraqi police and soldiers backed by armoured vehicles and military helicopters, pilgrims poured into the Shi'ite holy city, many after making a long journey by foot.
Iraq's Shi'ite-led government has tightened security for Arbaeen and an earlier ritual, Ashura, in recent years, but a peaceful event was especially important this year for Prime Minister Nuri al-Maliki ahead of April parliamentary elections.
"We deployed highly trained forces to form defensive cordons around Kerbala to abort any possible terrorist attack," Major-General Othman al-Ghanimi, chief commander of the Iraqi army in Kerbala told Reuters.
Arbaeen marks the end of a 40-day mourning period following Ashura, the religious ritual that commemorates the death of the Prophet Mohammad's grandson Imam Hussein in 680.
Shi'ites are considered apostates by hardline Sunni Islamist insurgents who have been regaining momentum in Iraq this year. On Thursday at least 36 people were killed in attacks targeting pilgrims ahead of Arbaeen.
This year has been Iraq's most violent since 2006-7, when tens of thousands died in strife between Sunnis and Shi'ites.
Sunni insurgents have targeted government buildings and security headquarters since the start of the year with apparently coordinated attacks involving suicide bombers on foot, car bombs and rockets, killing many hundreds.
Loudspeakers blared chants across Baghdad and Kerbala, 80 km (50 miles) south of the capital, where pilgrims dressed in black gathered outside the golden-domed Imam Hussein shrine.
Some pilgrims beat their heads and whipped themselves in an act of grief and mourning. Many had walked miles in processions that have been frequent target for Sunni Islamist insurgents.
"I came from Baghdad walking to attend Arbaeen in Kerbala and I don't care about terrorists. I'm not afraid of suicide bombers, and I tell them, 'Come and blow us up, we are willing to die for the sake of our rituals'," Ali Minati, wrapping up a flag portraying Imam Hussein, told the local Forat channel from Kerbala. (Editing by Alexander Dziadosz and David Evans)