BAGHDAD -- Four suicide bombers believed to be women struck a Shiite pilgrimage in Baghdad and a Kurdish protest rally in northern Iraq on Monday, killing at least 57 people and wounding nearly 300 in one of this year's deadliest attacks, police said.

Attacks carried out by women are becoming increasingly common, even as overall violence is at the lowest level in four years.

On Monday, three bombers believed to be women blew up their explosive vests in the middle of pilgrims in Baghdad moments after a roadside bomb attack, killing at least 32 people and wounding 102, Iraqi officials said.

In Kirkuk, 25 people were killed and 185 wounded when a blast tore through a crowd of Kurds protesting a draft provincial elections law, officials said.

Police spokesman Brig. Gen. Burhan Tayeb Taha said the Kirkuk bomber was also a woman, and that he had seen her remains at the site. The U.S. military confirmed a suicide bombing but said it had no indication the attacker was a woman.

Ryan Crocker, the U.S. ambassador to Iraq, and Gen. David Petraeus, the top U.S. commander in Iraq, condemned the attacks.

"The targets of these vicious and cowardly attacks were innocent Iraqi men, women, and children who were freely practicing their democratic rights and religious faith," their joint statement said. "It is crucial that the Iraqi people remain united and steadfast in the face of those terrorists who would use violence to destroy a free Iraq and set back the progress for which so many have so bravely sacrificed."

Authorities clamped a 3 p.m. to 6 a.m. curfew on Kirkuk, which is home to Kurds, Turkomen, Arabs and smaller groups. In Baghdad, the Iraqi military command imposed a citywide vehicle and motorcycle ban from 5 a.m. Tuesday to 5 a.m. Wednesday.

Iraqi security forces deployed about 200 women this week to search female pilgrims during a procession toward the northern Baghdad neighborhood of Kazimiyah, where an 8th century Shiite saint is buried.

The pilgrims are marking the death of Imam Moussa al-Kadhim, a Shiite saint interred under a golden domed shrine. Monday's attacks took place in the mainly Shiite Karradah district, which is several miles away from the destination of the pilgrimage in Kazimiyah. Most of the dead were women and children, police and health officials said.

"I heard women and children crying and shouting, and I saw burned women and dead bodies lying in pools of blood on the street," Mustapha Abdullah, a 32-year-old man who was injured in the stomach and legs, said from the hospital where he was being treated.

It was the deadliest attack in Baghdad in more than a month. On June 17, a truck bombing killed 63 people in Hurriyah, a neighborhood that saw some of the worst Shiite-Sunni slaughter in 2006.

In Kirkuk, the suicide bomber targeted Kurdish demonstrators who were protesting a provincial elections measure blocked in parliament because of disagreement over power sharing.

Maj. Gen. Jamal Tahir, a Kirkuk police spokesman, said police also found a car bomb nearby and detonated it safely.

After the explosion, dozens of angry Kurds opened fire on the offices of a Turkomen political party, which opposes Kurdish claims on Kirkuk.

A police official, speaking on condition of anonymity because he was not authorized to speak to the media, said no one was hurt in that attack and that the party offices were placed under police protection.

Since the 2003 ouster of Saddam Hussein, who was a Sunni, Shiite political parties have encouraged huge turnouts at religious festivals to display the majority sect's power in Iraq. Sunni religious extremists have often targeted the gatherings to foment sectarian war, but that has not stopped the Shiites.

In 2005, at least 1,000 people also were killed in a bridge stampede caused by rumors of a suicide bomber in Baghdad during the Kazimiyah pilgrimage.

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Associated Press writers Hamid Ahmed, Saad Abdul-Kadir and Qassim Abdul-Zahra contributed to this report.