BAGHDAD — A female suicide bomber struck a tent filled with women and children resting during a pilgrimage south of Baghdad on Friday, killing 40 people and wounding about 80 in the deadliest of three consecutive days of attacks against Shiite worshipers.
The assault, which also appeared to be the deadliest in Iraq this year, demonstrates the determination of some extremists to reignite sectarian warfare.
It also underscores how fragile the security situation remains, even as the United States turns over more responsibility to the Iraqis.
Witnesses said many of the injured were hurt in a stampede as survivors — most of them poor Shiites exhausted after days of walking — scrambled away from the tent in terror. They left behind piles of clothing, small rugs and toddlers' strollers.
"It was a horrific scene, with dead and screaming injured people on the ground," said Sadiya Kadom, 40, a Baghdad resident who was near the tent when the blast occurred.
No group claimed responsibility, but suicide bombings against Shiite civilians are the signature attack of al-Qaida in Iraq, which U.S. commanders say has been severely weakened but not defeated.
"What kind of belief system do these people have? Are they monsters?" a man shouted as he held his dazed and wounded son, wrapped in a red and yellow blanket.
The bomber was successful in detonating her explosives despite a massive security operation by Iraqi authorities to protect the hundreds of thousands of pilgrims streaming into the Shiite holy city of Karbala for religious rituals that culminate Monday.
The vast numbers of pilgrims and the distances many of them must travel make it all but impossible to guarantee their safety from determined extremist groups willing to die.
The blast occurred at midday alongside a railroad track close to Musayyib, about 40 miles south of Baghdad and 10 miles north of Karbala. Separate tents for men and women offer pilgrims food, beverages and a place to rest along the routes to Karbala.