A female suicide bomber walking among Shiite pilgrims in Baghdad detonated an explosives belt on Monday, killing at least 46 people and wounding more than 122, officials said.
The bombing was the first major strike this year against pilgrims making their way to the southern city of Karbala to mark a Shiite holy day. It came as security official warned of a possible increase in attacks by insurgents using new tactics to bypass bomb-detection methods.
The bombing raises fears of an escalation of attacks as hundreds of thousands of Shiites head by Friday to the southern holy city of Karbala to mark the end of 40 days of mourning following the anniversary of the death Imam Hussein, a revered Shiite figure.
The bomber hid the explosives underneath an abaya -- a black cloak worn from head to toe by women -- as she joined a group of pilgrims on the outskirts of Baghdad's Shiite-dominated neighborhood of Shaab, said Maj. Gen. Qassim al-Moussawi, Baghdad's top military spokesman.
The bomber set off the blast as she lined up with other women to be searched by female security guards at a security checkpoint just inside a rest tent, al-Moussawi said.
After clearing the security check, the women pilgrims were served water and sherbet, a police official said.
Another police official said 46 were killed and 122 were wounded. All the officials spoke on condition of anonymity because they were not authorized to talk to the media.
Witnesses described a chaotic scene in the minutes following the blast.
Raheem Kadhom, 35, was standing about 150 yards (138 meters) away when he says a huge fireball erupted among the pilgrims.
Pilgrims were "on the ground, covered in blood and crying for help," he said. "Banners were all over the ground and covered in blood."
The blast was so powerful it knocked some out of their slippers and shoes, which were scattered across the ground, Khadhom said.
Many ran to the aid of the pilgrims. Some put the wounded in cars, taking them to hospitals rather than wait from ambulances, Kadhom said.
Despite an overall decline in violence in Iraq, al-Qaida and other Sunni extremists have routinely targeted pilgrims in an attempt to stoke sectarian strife and weaken the Shiite-dominated government.
The vast numbers of pilgrims and the distances many of them must travel at predictable times of the year make it all but impossible to guarantee their safety against extremist groups. The pilgrims targeted Monday were walking from the northeast Diyala province and other areas north of Baghdad, police said.
During a pilgrimage last February, a female suicide bomber attacked a tent filled with women and children resting during the walk to Karbala, killing 40 people and wounding 60 others. A month before that, a suicide bomber dressed in women's clothing and hiding among Iranian pilgrims killed more than three dozen people outside a mosque in Baghdad's Shiite neighborhood of Kazimiyah.
Security forces were put on alert shortly after the attack, al-Moussawi said.
"We informed all checkpoints to be careful and to intensify the search procedures," he said.
Iraqi authorities lack enough policewomen to conduct searches at most checkpoints, and security forces have been reluctant to use bomb-sniffing dogs against people because of cultural sensitivities.
Al-Moussawi warned insurgent groups were using new tactics to smuggle explosives past security forces.
"Terrorist groups have come up with ways to hide explosive substances that cannot be detected with bomb detector sets," he said in a statement posted on his Web site.
Iraq's forces have been using a bomb-detection device at checkpoints across the country that Britain banned for export after questions were raised about whether it works. Iraqi security officials have insisted it works, though began their own investigation after the U.S. military also said the device did not work.
Meanwhile, Baghdad's military command has referred 134 members of Iraq's security forces for investigation of possible negligence for security lapses that allowed for last week's suicide bombing attacks against three hotels and Baghdad's main crime lab, al-Moussawi said.
Associated Press Writers Chelsea J. Carter and Qassim Abdul-Zahra contributed to this report.