The bomb was packed in a taxi abandoned on a route used by pilgrims visiting a Baghdad shrine to commemorate the anniversary of the death of Shi’ite imam Moussa al-Kadhim, a great-grandson of Prophet Mohammad, authorities said.  

It was the third attack targeting Shi’ite pilgrims this week and follows a wave of bombings on Wednesday in Baghdad and across Iraq that killed 70 people in the worst single day of violence since US troops left the country in December.  

Recent attacks on Shi’ite targets are reviving fears Iraq risks slipping back into broad sectarian violence, especially with Shi’ite, Sunni and ethnic Kurdish parties that make up its fragile government feuding over how they share power.  

The ceremonies began about 5am GMT at the shrine of Kadhim, who died in 799 and is said to have been poisoned, with a religious leader telling the story of the imam, while people in the crowd wept, an AFP journalist said.

Pilgrims then carried an empty coffin symbolising the imam to the shrine in the Kadhimiyah area of north Baghdad, repeating religious chants, with some hitting their heads and chests with their hands in a sign of mourning.

"More people are attending the commemoration this year than previous years," said Karim Mohammed, 52. "When we ... see that there are explosions, it becomes a challenge to us, so those who decided not to go will go."

Mohammed, who said he had walked for three days from Samarra, 110 kilometres (70 miles) north of Baghdad, had put mud on his face and on his black robe in a sign of mourning.

Security measures in Kadhimiyah were tight, with anti-terrorism special forces deployed in the area. Pilgrims were searched at various points, while helicopters flew overhead.

On Wednesday, 72 people were killed and more than 250 wounded in bomb and gun attacks across Iraq, with Al-Qaeda's local affiliate, the Islamic State of Iraq, claiming responsibility.

A car bomb exploded on the outskirts of Kadhimiyah on Wednesday, killing seven people, while another bomb blasted pilgrims' food tents in Karrada in central Baghdad, leaving 16 people dead.

Shi'ite pilgrimages were prohibited under the rule of Saddam Hussein, but they have attracted huge numbers of people in the years since his 2003 overthrow.

Along with the security forces, the Shi'ite majority in Iraq has been a main target of Sunni Arab armed groups since the fall of Saddam's Sunni-dominated regime.

Violence has declined dramatically since the 2006-2007 peak of sectarian bloodshed, but attacks remain common, especially in Baghdad. A total of 132 Iraqis were killed in May, official figures show.