WASHINGTON - A suicide bomber appears to have been responsible for Tuesday's deadly attack at an Army mess hall in Iraq, the top U.S. general said yesterday, raising new questions about the military's ability to keep soldiers safe even inside guarded American compounds.
The attack on Forward Operating Base Marez near Mosul in northern Iraq killed 22 people, including 18 Americans, and injured 69.
"At this point it looks like an improvised explosive device worn by an attacker," Gen. Richard B. Myers, chairman of the Joint Chiefs of Staff, said at a Pentagon briefing.
"I assure you that everything possible is being done to get to the bottom of what happened and to take the appropriate steps so we can prevent potential future attacks of this nature," Myers said.
An Islamic militant group linked to al-Qaida, Ansar al-Sunna, which is believed to operate in the Mosul area, claimed responsibility for the attack shortly after it occurred.
Myers did not say yesterday who he believed to be responsible and said he didn't know if the body of a non-American found at the site was the attacker's. U.S. military officials initially said a rocket was the most likely cause of the blast.
Without being specific, Myers indicated investigators had found remnants of the bomb. Military officials in Iraq said yesterday that shrapnel from the explosion included small ball bearings, which are often used in suicide bombings, the Associated Press reported. Bomb technical experts from the FBI assisted in the investigation of the blast site.
In Mosul yesterday, hundreds of U.S. troops spread out through the city and blocked five bridges over the Tigris River to civilian traffic. An Associated Press reporter said city streets were mostly deserted as personnel carriers and armored Humvees patrolled through Sunni Muslim neighborhoods.
"We are targeting certain objectives, geographical as well as intelligence information about the terrorists," said Lt. Col. Paul Hastings, spokesman for Task Force Olympia, the main force responsible for security in northern Iraq. "We are going to take the fight to the enemy."
Even before the likely cause of Tuesday's attack was known, analysts pointed out insurgents' increasing ability to gather intelligence on U.S. forces, giving them an understanding of American operations and vulnerabilities.
"We're operating in their neighborhood. They know what we do. ... They know when convoys are coming and going," said Jeffrey White, a former officer at the Defense Intelligence Agency who is an associate at the Washington Institute for Near East Policy.
Insurgents include former members of Saddam Hussein's security and intelligence services who would understand how to develop informers' networks, he said.
Although the identity of the attacker and the way he entered the base were unknown yesterday, a suicide bombing at a U.S. military base would have required a combination of skill, planning and intelligence.
A bomber would have had to penetrate base security and enter the mess hall tent with an explosive device attached to his body and remain undetected until the bomb went off. Such devices are commonly stitched into vests.
Analysts also said that with 120,000 Iraqis enlisted in the nation's security services, it's likely that at least a few of them have divided loyalties, with clan and ethnic ties pulling them toward providing valuable information to the insurgents.
Some of these Iraqi recruits guard U.S. bases and other facilities in Iraq. Many other Iraqis work with American agencies and companies as translators and guides.
"In Iraq's case, it seems likely that family, clan, and ethnic loyalties have made many supposedly loyal Iraqis become at least part-time sources [of intelligence for the insurgents]," Anthony Cordesman, strategic analyst at the Center for Strategic and International Studies, wrote in a report this week.
With Americans' urgent need to enlist and train Iraqi forces so they can bear more of the security burden, individual background investigations are cursory, he noted.
"U.S. vetting will often be little more than either a review of past ties or checks on the validity of data being provided," Cordesman wrote.
Insurgents are able to get a window on U.S. and Iraqi government operations from the resulting enlistees, he said.
"This will often provide excellent targeting data on key U.S. and allied officials, events," he wrote. "It can include leverage and blackmail, and vulnerability data, as well as warning of U.S. and other military operations."
U.S. facility defenses have been penetrated before. In October, a pair of bombings leveled a restaurant and damaged a market inside the protected Green Zone, prompting officials to launch a security review.
Responsibility for that attack was claimed by Abu Musab al-Zarqawi, a Jordanian Islamic militant who is Iraq's most-wanted man. Witnesses said at the time that two bombers carried backpacks and spent time sipping tea in a cafe before striking.
Myers and Defense Secretary Donald H. Rumsfeld described measures being taken to protect U.S. troops in Iraq, but both pointed out the difficulty in preventing suicide attacks by determined insurgents.
Troops train in bomb detection, study enemy attacks and update their own tactics, Myers said. "Additionally, we continue to use technological advances such as unmanned aerial vehicles and remote sensors," he said.
Separately, military officials in Iraq said a hardened mess hall was being built at the base.
But in the conflict against insurgents in Iraq, Myers said, "The front line can be the dining hall, it can be the road outside the base, it can be the police station or the governor's office or the mayor's office down in Mosul. That's [the insurgents'] territory. They operate all over that. They can wear, and they do wear, clothes like every other Iraqi."
Data on casualties
In a new breakdown yesterday of those killed and wounded in Tuesday's attack, the U.S. military command in Baghdad lowered the number of U.S. servicemen killed, from 15 to 13.
In addition, the dead included five U.S. civilians, three Iraqi National Guard members, and one "unidentified non-U.S. person." Of the wounded, 44 are members of the U.S. military, seven are U.S. contractors, five are Defense Department civilian workers, two are Iraqi civilians, 10 are contractors of other nationalities, and one is of unknown nationality.
The Associated Press contributed to this article.