The attacker targeted a tent where women and children were resting about 25 miles south of Baghdad. Most of those killed and injured were women and children, witnesses and police and hospital officials told the New York Times.
The attack, which occurred during one of the holiest events of the Shiite calendar, appeared to be aimed at stoking sectarian violence, Iraqi and Western officials said.
It came a day after a bomb killed eight in the Shiite holy city of Karbala, to which hundreds of thousands were headed to observe Arbain, one of the most important Shiite Muslim rites. The ritual marks the end of a mourning period after the anniversary of the death of the Prophet Muhammad's grandson, Imam Hussein, in the seventh century.
Shiite religious rites have drawn huge crowds since the toppling of the Sunni-led government of Saddam Hussein, who curtailed large Shiite gatherings. Iraqi officials have mounted an extensive security operation to protect the pilgrims.
Imam Hussein was killed in a battle near Karbala for the leadership of the nascent Muslim nation following Muhammad's death in 632. His death led to the split between Sunni and Shiite Muslims.
The Arbain rite, which culminates early on Monday, is difficult to secure. Many pilgrims walk the entire way to Karbala, and are easy targets as they cover hundreds of miles clutching religious banners.
The suicide bomber apparently tried to pass through the center of Abu Jasim village in al-Musaib, a popular resting place for pilgrims, a local police official told the Times. When she could not get past a checkpoint, the attacker went to the tent and set off the explosives.
Abu Islam, 40, said he heard a huge explosion about 11:30 a.m. and went outside only to confront a scene of destruction.
"I went out very quickly and saw two tents on fire," he said. "Burned corpses were everywhere. But mostly kids and women because the bomber targeted the tents of women."
About 40,000 Iraqi troops have been deployed along major routes to Karbala, and officials say security cameras have been installed near the shrine to keep a lookout for possible threats.
"I have been sleeping in the ambulance," emergency worker Ahmed Kadhom said.
The events have been regular targets of Sunni insurgents such as al-Qaida during the sectarian bloodshed that followed Saddam's fall from power. Al-Qaida views Shiites as heretics. A suicide attack during Arbain last year killed 63 people.
"These cowardly actions will not undermine the determination and patience of the pilgrims. We call upon our people and especially the security forces to take more precautions and be alert," said a statement on the Web site of Ayatollah Sadiq al-Husseini al-Shirazi, a member of Iraq's top Shiite clergy.
Last March, a female suicide bomber attacked Shiite worshippers in Karbala, killing at least 49. At least 85 people died in a suicide bombing in Karbala in March 2004.
The chief United Nations official in Iraq, Staffan de Mistura, has said the attacks against pilgrims were "clearly designed to sectarian tensions" that many Iraqis hope are behind them.
Militants often use women for suicide bombings since they are less likely to be thoroughly searched by male guards, and because their voluminous robes can easily conceal vests packed with explosives and shrapnel. Iraqi police and troops have responded by trying to hire more women as security officers to search women at checkpoints.
A recent sharp drop in violence helped allies of Prime Minister Nouri al-Maliki score victories in the Shiite south in local elections last month. However, the security gains are fragile, and the threat of suicide and car bomb attacks remains.
Security sources have also warned that there could be an increase in attacks after al-Maliki's strong electoral showing, as political rivals and militants try to undermine the perception that the insurgency is on its last legs.
Earlier in the week, there were four separate attacks on pilgrims in Baghdad, killing at least 20 people and injuring 71. On Friday, pilgrims were also attacked outside the city of Hilla, south of Baghdad, when an unidentified gunmen opened fire, killing two people.