A female homicide bomber struck Shiite pilgrims south of Baghdad on Thursday, killing 26 people and wounding scores of others after the government announced new measures to protect worshippers ahead of a major religious festival.

Also Thursday, the U.S. military announced that six Navy guards face trial for allegedly assaulting prisoners and releasing pepper spray into a cellblock following a disturbance at the main U.S. prison in Iraq.

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The woman detonated her explosives among a group of pilgrims resting by the side of a road in Iskandariyah, a former Sunni insurgent stronghold 30 miles south of Baghdad. Women were cooking dinner, men were praying and children were playing nearby when the attacker struck, a witness said.

"Minutes after I passed the resting spot, I heard a big explosion. I turned my head and saw big flames," said Ahmed al-Saadi, a 34-year-old carpenter from Sadr City in Baghdad. "We rushed to the scene and saw charred bodies, while wounded people were crying for help. Pots and burned prayer rugs were scattered all the place."

At least 75 people were injured in the blast, said a senior provincial security official who spoke on condition of anonymity because he wasn't authorized to release the information. He said police believed the bomber was a woman based on witness reports.

The pilgrims were marching to the Shiite holy city of Karbala, 50 miles south of Baghdad to celebrate the birth of Mohammed al-Mahdi, the 12th Shiite imam, who disappeared in the ninth century.

Devout Shiites believe he will return to restore peace and harmony. The ceremonies reach their high point this weekend.

Witnesses interviewed in an Iskandariyah hospital spoke of horrific scenes of mangled flesh and screaming victims.

Khazim Jabir, 39, from the Baghdad neighborhood of Hurriyah, said he was walking near a group of pilgrims receiving food and water when he heard a thunderous explosion.

"Seconds later, I saw fire and flaying pieces of flesh," he said. "I fell down and I was able to see one of my legs bleeding. People were running in all directions."

Yassir Ibrahim, 28, also from Baghdad, said his hands were injured by the blast.

"I don't understand the reason for attacking us," he said. "We were only heading to a holy place."

Earlier Thursday, at least two people were killed and 16 wounded in a pair of small bombings in Baghdad that police believed were targeting pilgrims.

Every year since the 2003 collapse of Saddam Hussein's Sunni-dominated regime, hundreds of thousands of Shiites have celebrated religious festivals — which have often been targeted by Sunni extremists.

Last month, three women homicide bombers attacked Shiite pilgrims during a festival in Baghdad, killing at least 32 people and wounding more than 100.

No group claimed responsibility for the Thursday blast but attacks on Shiites have been associated with the Sunni extremist Al Qaeda in Iraq.

However, U.S. spokesman Lt. Col. Steven Stover said at least one of the Baghdad bombings was believed carried out by Iranian-backed Shiite extremists "in an attempt to heighten public unrest."

With security concern on the rise, the Iraqi military announced a series of measures aimed at protecting pilgrims and tamping down sectarian tensions during the festival period.

Iraqi military spokesman Brig. Gen. Qassim al-Moussawi said members of the Shiite-dominated security force were banned from placing religious posters on their vehicles or joining pilgrims in chanting Shiite slogans — moves that might provoke Sunnis.

Al-Moussawi said pilgrims must not carry weapons and travel by foot after sundown. He also warned pilgrims to avoid rumors that could spread panic or accept food from strangers.

In Karbala, police deployed about 2,000 additional troops in the city. Bikes and motorcycles were also banned from the center of the city around the two major religious shrines.

The charges against the six Navy guards were in connection with a May 14 incident at Camp Bucca, the biggest American detention facility near the Kuwaiti border, according to Navy spokeswoman Cmdr. Jane Campbell.

Trouble started when several guards were attacked by detainees, who spit and threw containers of human waste at them, Campbell said.

Two detainees were allegedly beaten and eight others were locked overnight in a cell which was filled with pepper spray and the ventilation was shut off, she said.

Seven other sailors received nonjudicial punishment for failing to report the incidents, Campbell said. Two had their charges dismissed while others were reduced in rank or faced suspended punishment, she added, declining to be more specific.

Trials for the other six are expected to be held within 30 days, Campbell said. Camp Bucca houses about 18,000 of the 21,000 detainees held by the U.S. in Iraq.

Treatment of detainees drew international criticism in 2004 with the release of pictures of grinning U.S. soldiers posing with detainees at the Abu Ghraib prison west of Baghdad. Some were naked, being held on leashes or in painful and sexually humiliating positions.

That prison has since been closed, and 11 U.S. soldiers were convicted of breaking military laws. Five others were disciplined in the scandal.

Abu Ghraib has been closed, and the U.S. has announced a series of reforms of the detention system, including Muslim religious training by moderate imams of younger inmates deemed less extreme in their views.

Last month, the military confirmed that Iraqi detainees had maintained self-styled Islamic courts and tortured or killed inmates who refused to join them. U.S. officials said the problem was centered at Camp Bucca.

Also Thursday, three policemen were killed and six others wounded in a bombing near Buhriz, a town about 35 miles north of Baghdad.

Farther north, in the city of Mosul, gunmen shot dead an off-duty policeman and army soldier in separate incidents.