Sniper attacks have sparked anger and panic among crowds of Shi’ite pilgrims in Baghdad. At least 15 people are reported killed and over 200 injured. Four suspected gunmen were shot dead by Iraqi police.
One flashpoint came as Shi’ites walked through a Sunni neighbourhood.
There had been fears sectarian violence of this kind would break out at the pilgrimage, which last year saw almost 1,000 people die in a mass stampede triggered by rumours of a suicide bomber.
In a bid to prevent car bomb attacks, all vehicles have been banned from the streets and police are carrying out random searches of the hundreds of thousands of faithful travelling to the shrine.
The focus of their attention is the burial site of eighth century Imam Moussa Kadhim, who Shi’ites believe was poisoned by a Sunni caliph.
The rivalry between Sunnis and Shi’ites, which predates Imam Moussa Kadhim, is more intense than ever in today’s Iraq and has fuelled fears the country could be sliding towards civil war.