Insurgents killed four more US troops in Iraq as warplanes destroyed two bomb factories on Tuesday in a bid to cut insurgent supply lines into Baghdad, where bombings continue to defy an armed crackdown.
One soldier died from a suicide truck bombing in the contested northern oil capital of Kirkuk that targeted a police station where American forces were visiting at the time, and damaged a girls' primary school.
The bomb - hidden under packs of flour in a new tactic designed to lull victims into a false sense of security - killed 13 Iraqis, including eight schoolgirls and a toddler. Another two American soldiers were wounded.
The second soldier died on Monday in a roadside bomb blast alongside his vehicle during combat operations near Baghdad, while a third soldier and a marine were killed in fighting in the western Anbar province on Monday.
The rising body count that shows no sign of relenting four years after the American military invaded Iraq to oust Saddam Hussein is fuelling growing opposition to the war in the United States and calls for troops to come home.
The latest fatalities brought US military losses in Iraq since the March 2003 invasion to 3,254, according to Pentagon figures.
Since the launch of a massive security operation in Baghdad in February, Iraqi and US troops have reduced execution-style killings in the capital, but car bombings carried out by suspected militants remain a major headache.
In a bid to stem the flow of explosives into Baghdad, the military is now focusing on detecting bomb-making facilities largely on the outskirts.
Aircraft on Tuesday destroyed two large buildings which the Americans said were used to manufacture and store explosives in the town of Arab Jubur, south of the capital.
"Ground forces called in for air support when they found large amounts of chemicals and improvised-explosive-device making materials in two buildings," the military said.
In an operation targeting presumed Al-Qaeda fighters near Anbar's former rebel town of Fallujah, a US warplane killed six "terrorists" in an air strike while forces on the ground arrested another seven, the military said.
Another group of Iraqi workers was abducted overnight in the flashpoint province of Diyala, less than 24 hours after the bodies of 21 Shiites snatched in similar circumstances were found.
The nine electrical company employees were kidnapped at gunpoint on their way home from work near Khalis, a Shiite town repeatedly bombed by presumed Sunni extremists in their campaign of sectarian violence.
US President George W. Bush, who has vowed to veto Congressional demands for most troops to withdraw within 12 months, spoke to Iraqi Prime Minister Nuri al-Maliki on pressing home the security crackdown to the end.
"Both leaders agreed on the importance of the present security plan for Baghdad and other areas of Iraq and agreed that these plans must be carried out until lasting success can be achieved," said a White House spokesman.
Gordon Johndroe also said Maliki had assured Bush he would "press forward" on key legislation such as a reform bill to encourage Sunnis back into mainstream politics and away from fighting.
Other attacks killed three civilians in Baghdad and three policemen in other cities on Tuesday, in a toll considerably less than the daily body count reported by security officials in recent days.