BAGHDAD: A female suicide bomber walking among Shiite pilgrims in Baghdad detonated an explosives belt on Monday, killing at least 41 people and wounding more than 100, officials said.

It 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 raised fears of an escalation of attacks when the pilgrimage culminates on Friday.

The bomber hid the explosives underneath an abaya — a women's black cloak that covers from head to toe — as she joined a group of pilgrims on the outskirts of the Shiite-dominated northern neighborhood of Shaab, said Maj. Gen. Qassim al-Moussawi, Baghdad's top military spokesman.

A police official and Baghdad hospital officials said 41 died, including a number of women and children, and 106 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.

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.

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.

This week, hundreds of thousands of Shiites make the pilgrimage to Karbala to mark the end of 40 days of mourning that follows Ashoura, the anniversary of the death Imam Hussein, one of two revered Shiite figures buried there.