BAGHDAD, Iraq - In the bloodiest attack on U.S. forces since the invasion of Iraq, a deafening explosion tore through a mess tent yesterday at a U.S. military base near Mosul, killing at least 22 people and wounding more than 60.
At least 15 U.S. soldiers and an unspecified number of American private contractors, Iraqi soldiers and foreign workers died in the lunchtime explosion, the cause of which was under investigation.
Early reports suggested a mortar or rocket attack, but a U.S. official said it was possible that an explosive device was placed at the scene. A fundamentalist Islamic group with links to al-Qaida later claimed responsibility and implied that a suicide bombing had taken place.
Officials in Baghdad placed the U.S. military death toll as high as 19. Seven other victims worked for the engineering firm KBR or a subcontractor, said a spokeswoman for Halliburton, KBR's corporate parent.
The blast struck hardest at soldiers lining up to get trays and utensils before entering the chow line, a witness said. The force knocked soldiers off their feet and out of their seats, and a giant fireball enveloped the top of the canvas-and-metal tent, according to an account by an American reporter embedded at Forward Operating Base Marez, a sprawling camp at the northern city's airport.
After the blast, scores of troops crammed into concrete bomb shelters, while others wandered around in a daze and collapsed, said Jeremy Redmon, an embedded reporter for the Richmond (Va.) Times-Dispatch.
"I can't hear! I can't hear!" a female soldier cried as a friend hugged her.
A huge hole was blown in the roof of the tent, and puddles of blood, lunch trays and overturned tables and chairs covered the floor, Redmon reported.
President Bush, visiting wounded troops at Walter Reed Army Medical Center in Washington, offered prayers and condolences for the families of those killed. He called the attack "particularly sorrowful for the families as we head into the Christmas season."
"We just want them to know that the mission is a vital mission for peace," Bush said.
Bush's words came a day after he acknowledged that the handover of security duties to Iraqi forces is taking longer than the United States had anticipated, mostly because many Iraqi soldiers and police have proven incapable of standing up to the insurgents.
Iraqi leaders and their American counterparts say they are committed to holding national elections Jan. 30 and vow that enough of Iraq will be stabilized to hold a credible vote. But attacks since Sunday in four different cities in four different provinces - Najaf, Karbala, Baghdad and Mosul - have killed nearly 100 people and deepened fears among the would-be Iraqi electorate.
British Prime Minister Tony Blair acknowledged those fears yesterday during a surprise visit to Baghdad. Calling the conflict a battle between democracy and terrorism, Blair praised Iraqi electoral workers who are being targeted by insurgents determined to chase out American forces and topple the Iraqi government that the U.S.-led coalition installed after the fall of Saddam Hussein.
"Here are people who are risking their lives every day in order to make sure that the people of Iraq get a chance to decide their own destiny," Blair said at a news conference after meeting with interim Prime Minister Ayad Allawi. "You can feel the sense of danger people live in. ... I feel a sense of humility."
Blair, making his first visit to Baghdad but his third to Iraq, vowed that the Iraqi forces and their British and U.S. backers would defeat the insurgency. Allawi, who warned Monday that the guerrillas were trying to foment a war among Sunnis, Shiites and Kurds, again rejected calls for the elections to be postponed and said a rise in violence was expected ahead of the vote.
Though suicide bombings and other guerrilla attacks routinely kill dozens of Iraqi civilians and security forces, yesterday's bombing was the single deadliest attack on Americans since Nov. 15, 2003, when a pair of Black Hawk helicopters came under fire over Mosul and collided. That crash killed 17 soldiers and wounded five.
But the total casualties at Mosul yesterday - at least 84 dead or wounded, including some civilians - outnumbered those suffered in any single incident aimed at Americans since the war began.
Mosul has been especially dangerous since early last month. Attacking police stations and assassinating government officials, guerrillas have targeted anyone they deem to be collaborating with the U.S.-led forces they consider occupiers. Nearly 100 bodies have been found in and around the streets of Mosul in the past few weeks. Many local police officers have quit.
The cause of yesterday's explosion at the Marez base was under investigation early today, and FBI experts were expected to arrive at the base overnight, said Lt. Col. Paul Hastings, a military spokesman near Mosul.
Initial reports indicated a mortar or rocket attack, and officials were pursuing that possibility. But Hastings said the bombing appeared to be a single explosion that might have been set off at the scene, perhaps involving a device smuggled into the camp.
The mess hall, a heated tent nearly the size of a football field, is the geographical and social center of the base. It can serve thousands of soldiers at a time, and soldiers often gather there to watch movies or sporting events on televisions scattered about the tent.
A new dining hall designed to be less vulnerable to rockets and mortars is under construction about a quarter-mile away.
The possibility of a mortar hit on the dining tent is constant, soldiers at Marez say, and often during mealtimes the thud of incoming fire can be heard.
The soldiers usually go on eating without pause.
Yesterday, hundreds of soldiers had just come for lunch when the blast hit, according to witnesses.
Afterward, tiles on the floor near the serving line "were covered with so much blood you couldn't see what color the tiles were," Capt. Pat Roddy of Fort Lewis, Wash., told The New York Times. "At least 50 percent of the tables and chairs had been obliterated by shrapnel."
Outside, "there were half-burned boots, not attached to any soldier, and you could see blood trails coming past the concrete barriers," Roddy said.
The Marez base was used by the Iraqi National Guard and other Iraqi forces as well as by American troops. Iraqi and U.S. officials acknowledge that insurgents have infiltrated Iraqi military units.
A radical Sunni Muslim group, the Army of Ansar al-Sunna, claimed responsibility for the attack. The group has been linked to several high-profile abductions and slayings. It claimed responsibility for the slayings of 11 Iraqi soldiers it captured and a dozen Nepalese security officers. The victims were either beheaded or executed by gunshot.
The Chicago Tribune is a Tribune Publishing newspaper. The Associated Press contributed to this article.