The bomber detonated his explosive vest after a policeman stopped him from approaching the pilgrims in the town of Balad Ruz, 90 km (55 miles) northeast of Baghdad, the Diyala province security operations center and a police source said.

The blast happened in the run-up to Ashura, the Shiite commemoration of the death of the Prophet Mohammad’s grandson Hussein at the battle of Kerbala in 680 AD. The event defines Shi’ism and cemented its rift with Sunni Islam.

While overall violence in Iraq has dropped sharply since its height in 2006-07, bombings and attacks still occur daily as security forces battle a stubborn insurgency.

On Sunday a suicide car bomber killed 13 people and wounded dozens near government buildings in the mainly Sunni city of Ramadi in western Iraq. Earlier this month a series of explosions — two of them targeting Iranian pilgrims — killed a total of 13 people and wounded at least 80.

Dozens of Shiite pilgrims have been gathering this month to mark Ashura, which is due to take place on Friday.