A double suicide bombing against Shia pilgrims killed more than 100 people as Sunni militants tried to incite Shia militias to break their adherence to the US and Iraqi forces’ Baghdad security plan.

The attackers blew themselves up on a packed street in Hilla, south of Baghdad, as Shia pilgrims marched to the shrine city of Karbala for this weekend’s religious holiday of Arbaeen.

Police put the death toll at 77, but hospitals said that at least 115 people had died and more than 200 had been wounded. According to the Iraqiya state television channel, the first bomber detonated his explosives while the second waited to strike until more people had rushed to administer first aid.

The attack was one of several against tens of thousands of Shias descending on Karbala for a festival that has become an expression of Shia power in the post Saddam Hussein era.

In the Baghdad suburb of Dura, insurgents fired rifles and launched mortars at the faithful marching to Karbala. Eight Shia pilgrims in the suburb were hit by gunmen who sprayed the worshippers’ minibus with bullets.

The unrest occurred as the Baghdad security plan ended its third week, with political leaders of the radical Shia cleric Hojatoleslam Moqtada al-Sadr’s movement chafing at the Government’s decision to cede security in Baghdad to Iraqi and American forces.

Hojatoleslam al-Sadr’s Mahdi Army militia has been blamed widely for death squad killings against Sunnis, which have stoked sectarian tensions. Since the latest campaign to reclaim the capital, Shia militants have desisted from their hunt for suspected Sunni terrorists.

Sadrist MPs voiced their discontent about the pressure from the Government for the Mahdi Army to stick to the sidelines, and considered the carnage in Hilla to be a direct result of the policy.

Previously Shia groups had “played a role in protecting the pilgrims and the attacks were fewer and less effective, but this year things are different,” said Bahaa al-Araji, a Sadrist MP. “The Government bears some responsibility for this because it has not provided enough security forces to protect the pilgrims,” Mr al-Araji said. “This indicates some shortcomings in the Baghdad security plan.”

Mr al-Araji spoke as US forces continued to search homes for weapons in his movement’s powerbase, the Baghdad district of Sadr City. The Sadrists are also in danger of having their six Cabinet ministers replaced as part of a government shuffle that Nouri al-Maliki, the Prime Minister, promised within two weeks.

US forces find themselves caught between the country’s Shia majority and Sunni population. Nine soldiers were killed on Monday, including six in a bomb attack in Salahuddin province, north of Baghdad.

Holiest of days

— Arbaeen is one of the holiest days in the calendar of Shia Islam

— It marks the end of 40 days of mourning for the death of Imam Hussein, the grandson of the Prophet Muhammad

— Imam Hussein was beheaded by a Sunni caliph after the Battle of Karbala, in AD680

— The battle was a contributing factor to the Sunni-Shia schism of Islam and is also commemorated by Sunnis

— Thousands of pilgrims travel annually to Karbala, where Imam Hussein's shrine is to be found, to join Arbaeen commemorations

— Passion plays, poetry and songs of mourning celebrating Imam Hussein are performed by Shias throughout the world during Arbaeen

Source: Times archives

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