Baghdad ? Suicide bombers, including at least three women, struck Shiite pilgrims in Baghdad and Kurdish protesters in the northern city of Kirkuk on Monday, killing at least 57 people – a brutal reminder that mass gatherings remain vulnerable despite vast improvements in security.

The attacks came even though the U.S. has stepped up efforts to recruit and train women for Iraq’s police force and enlist them to join Sunnis fighting al-Qaida. Insurgents increasingly use female bombers because their billowing, black robes easily hide explosives and they are less likely to be searched.

U.S. military figures show at least 27 female suicide bombings this year, compared with eight in 2007.

Monday’s attacks tapped into two different sets of fears.

The three nearly simultaneous bombings in Baghdad undermined public confidence in recent security gains that have tamped down sectarian bloodshed. The attack in Kirkuk, 180 miles to the north, showed that ethnic rivalries can turn into mass slaughter in a city that is home to Kurds, Turkomen, Arabs and other minorities.

The attack in Kirkuk killed at least 25 people and wounded 185, a police spokesman said.

The Baghdad bombings left piles of rubble and shattered glass on the streets alongside crumpled cars and sandals from panicked pilgrims, many of whom had slept at rest areas before rising at dawn to begin their annual march to the golden domed shrine of Imam Moussa al-Kadhim.

At least 32 people were killed and more than 100 were wounded, Iraqi police and hospital officials said. It was the deadliest attack in the capital since June 17, when a truck bombing killed 63 people in Hurriyah.

In a throwback to more violent times, the Iraqi government announced a 24-hour curfew in Baghdad, banning all vehicle movement starting 5 a.m. today.

At least 478 Iraqi civilians have been killed in violence so far this month, representing a 76 percent decline when compared with July 2007, when the death toll was 2,021, according to an Associated Press count.