Four female suicide bombers killed at least 57 people in two separate attacks in Iraq today, targeting a major Shia pilgrimage in Baghdad and a Kurdish political protest in the northern city of Kirkuk.

The carnage, which also left almost 300 people injured, was the among the worst the country has seen in months, challenging recent security gains that have pushed violence down to its lowest level in four years.

In the bloodiest attack, three women blew themselves up amongst thousands of pilgrims gathering in the capital to mark the death of an eighth century religious figure.

Up to 32 people were killed and more than 100 wounded in the coordinated blasts that ripped in close succession through the central district of Karradah.

Female bombers have become the weapon of choice for al-Qaeda in recent months because they are less likely to be searched at checkpoints, which are typically guarded by men.

The black Islamic robes often worn by women are also easy garments to conceal an explosives vest without attracting attention. More than 20 female suicide bombings have been carried out in Iraq this year.

Several hundred female guards have been deployed across Baghdad to frisk women taking part in the pilgrimage, but the number appears insufficient given that up to one million people are expected to flock to the Khadamiya shrine for the festival, which climaxes tomorrow.

The triple bombings caused scenes of chaos that used to be a daily occurrence in the capital before a security crackdown by US and Iraqi forces.

Ambulances rushed to ferry off the wounded and the dead, which included women and children. Police cars also helped to carry the victims because there were too many for the ambulances to manage. Local people were seen clearing away the blood.

No one has claimed responsibility for the explosions but al-Qaeda has in the past targeted major Shia religious festivals and anniversaries.

The Khadhamiya pilgrimage was marred in 2005 by one of the worst losses of life in a single incident since the 2003 invasion. Up to 1,000 people died when rumours of a bomb attack triggered a stampede among pilgrims crossing a bridge leading to the shrine.

Despite the multiple bombings, tens of thousands of pilgrims continued to flood through the streets of Baghdad heading for the revered shrine in the north of the capital.

Waving red, black or green flags, they passed through numerous police check-points. Tents also lined the route, offering people shelter from the scorching sun and refreshments.

One woman said nothing would deter her from visiting the shrine. "The pilgrims killed will go to heaven because they are martyrs and the criminals who killed the pilgrims will go to hell,” said Um Shakir, a retired teacher, 50.

Away from the Shia pilgrimage, the bombing in Kirkuk targeted thousands of Kurds who were protesting against a draft provincial elections law that is being debated in Parliament.

The blast, about 100 metres away from the offices of the provincial government, prompted a stampede as police shot in the air. At least 25 people were killed and 185 wounded.

Afterwards, protesters used stones and sticks to attack shops in the area owned by non-Kurds. They also stormed the offices of three opposition political parties. A curfew has since been imposed until 7am tomorrow.

Kurdish objections over a proposed power-sharing formula on the provincial council in Kirkuk have blocked the law from being passed. Many Kurds consider oil-rich Kirkuk to be part of their historical land.

The city is home to Kurds, Turkomen, Arabs and smaller ethnic groups.

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