The United States military in Iraq says a marine and nine soldiers have been killed in Iraq, including four in a roadside bombing near Baghdad.
US troops are more exposed as they try to tackle sectarian strife
The blast struck the soldiers' vehicle as they travelled west of the capital.
Three more were killed in the restive Diyala province, north of Baghdad. The three others died in separate attacks.
The deaths come as US-led forces in Iraq experience a surge in casualties in insurgency attacks; more than 60 US troops have been killed this month.
The BBC's Andrew North in Baghdad says that, with an average of three Americans dying every day, this is one of the highest casualty rates sustained by US troops since January 2005.
The US military gave no further details about the deaths in Diyala, apart from saying they occurred during operations in the province.
All the fatalities happened on Tuesday. The US military usually announces deaths the following day.
One soldier died in northern Baghdad when his patrol was attacked with small-arms fire. Another was killed when his patrol was hit by a roadside bomb.
In western Anbar province, a marine died from his wounds after coming under fire, the military said.
Commanders say American troops are more exposed to attack at the moment because of stepped-up operations to tackle sectarian violence in Baghdad and elsewhere.
The sharp increase in deaths comes as debate intensifies in Washington and Iraq over possibilities of a new strategy for addressing the worsening security situation.
On Tuesday, at least two special police commanders were moved from units at the centre of allegations about Shia death squads carrying out sectarian killings of Sunni Muslims.
Interior Ministry officials played down the significance of the changes in public, but privately said they were the result of US and Sunni pressure.
There have been widespread allegations of the involvement in Iraqi policemen in the sectarian killings carried out by death squads and illegal militia.