Insurgents also killed at least 14 other Iraqis across the country, and kidnapped an Iraqi police general, Khodr Abbas al-Salihi, in Baghdad.
The six US soldiers died and six others were wounded in three rebel attacks on Tuesday, the military said.
The last three weeks have been one of the bloodiest period for the US forces in Iraq with about 50 soldiers killed across the war-torn country.
Four died and six were wounded when insurgents ambushed their patrol vehicles near the northern oil town of Baiji, the military said, adding that rebels set off a mine and opened fire with guns.
The attack was claimed by al Qaeda's frontman in Iraq Abu Musab al-Zarqawi, according to an unverified Internet statement.
A fifth soldier was killed by a suicide car bomber in the capital, while a sixth died by small arms fire during combat operations near Habbaniyah in north-west Iraq.
The latest casualties came hours after US Defence Secretary Donald Rumsfeld accused Iran of allowing sophisticated bombs, including more lethal 'shaped' charges, to be smuggled across its border into Iraq.