BAGHDAD A radical Islamist group thought to be a front for al Qaida in Iraq has claimed responsibility for a Friday suicide bombing that killed five U.S. soldiers in the northern city of Mosul.
The attack, the single deadliest to befall Americans here in more than a year, also killed two Iraqi national police officers.
In statements posted Monday on extremist Web sites, the Islamic State of Iraq said it planned and carried out the bombing. The group also claimed responsibility for a suicide attack that killed at least nine U.S.-allied Sunni Muslim militiamen in Southern Iraq on Saturday.
The Islamic State of Iraq is regarded by the United States as a front group for al Qaeda in Iraq, though ISI describes itself as a coalition of several extremist organizations. In 2006 ISI declared an Islamic state in Iraq's Sunni Muslim areas.
U.S. officials have said that al Qaeda in Iraq has been so severely weakened over the past year or so that it probably can no longer carry out the massive attacks it once perpetrated.
But last week's bombings, in combination with a wider upswing in violence over the past two months here, cast doubt on those assertions.
In Monday's Web postings, ISI said the attacks were part of a plan that the group announced last month to target Americans and their supporters, which ISI dubbed the "Plan of Good Harvest.
"Our brother cried Allah is Great' and he detonated his truck amidst a large gathering of crusaders and apostates, tearing them apart, one of the postings said. "We ask Allah to accept our brother as a martyr and to place him in the highest rank of paradise.
The postings were translated by SITE Intelligence Group, a Maryland-based company that monitors extremist Web sites.
U.S. officials did not immediately respond to requests for comment on ISI's claims.
Ali Ghaidan, the Iraqi Army's top ground commander, dismissed the idea that the attacks may be a sign that al Qaeda in Iraq is regaining strength.
"Al Qaeda is losing, Ghaidan said. "Even though they cause explosions here and there, they are bankrupt and they are being kicked out of this country.
U.S. military officials said the five Americans who died in the Friday bombing were simply targets of opportunity and that the bomber's true aim was an Iraqi national police station where the attack took place. The U.S. soldiers who died were in a convoy that was passing the police station at the time of the explosion.
The attacker drove a dump truck packed with at least 200 pounds of explosives into a barrier just outside the national police station. More than 60 people were injured.
The Americans who died were assigned to the Army's 1st Battalion, 67th Armor Regiment, 2nd Brigade Combat Team, 4th Infantry Division, out of Fort Carson, Colo.
The Department of Defense identified them Sunday as Staff Sgt. Gary L. Woods Jr., 24, of Lebanon Junction, Ky.; Staff Sgt. Bryan E. Hall, 32, of Elk Grove, Calif.; Sgt. Edward W. Forrest Jr., 25, of St. Louis, Mo.; Cpl. Jason G. Pautsch, 20, of Davenport, Iowa; and Pvt. Bryce E. Gautier, 22, of Cypress, Calif.
In the Saturday bombing, a suicide attacker wearing an explosives vest assaulted a crowd of militiamen waiting for their paychecks near Iskandariyah, about 40 miles south of Baghdad.
The militiamen targeted are known as the Sons of Iraq, which the U.S. military launched with the help of local tribal leaders in 2007. Many of the militia's members are former Sunni insurgents who helped kill Americans until the U.S. began paying them two years ago to turn against violence and help root out al Qaeda in Iraq.
The Sons of Iraq program is credited with playing a major role in the steep reduction in violence across Iraq over the past year or so. Al Qaeda frequently targets the militia's members.
U.S. troops are scheduled to withdraw from Iraqi cities in less than two months and President Barack Obama has pledged to pull most Americans from the country altogether by the end of next summer. The recent uptick in attacks here has raised concerns about what might happen when the U.S departs.
Also on Monday, an American soldier was killed when an armor-piercing bomb struck a U.S. convoy south of Baghdad, the military said in a statement. The soldier's name was withheld pending notification of relatives.
McClatchy special correspondent Hussein Kadhim contributed to this story.