The soldiers were conducting a patrol to clear a route so that another unit could move through the area on Saturday, the military said in a statement. A bomb exploded near one of their vehicles, the statement said.
The toll raised to 57 the number of Americans killed in Iraq in December. At least 2,945 members of the U.S. military have died since the U.S.-led invasion in March 2003, according to an Associated Press count.
On Saturday, Iraq's prime minister reached out to Sunni Arabs at a national reconciliation conference, urging Saddam Hussein-era officers to join the new army and calling for a review of the ban against members of the former dictator's ruling party.
But key players on both ends of the Sunni-Shiite divide skipped Saturday's meeting, raising doubt that the conference will succeed in healing the country's wounds.
At least 23 people were killed Saturday in Iraq, including a Sunni cleric and a Sunni politician who were shot to death in Iskandariyah, south of Baghdad. Police also found the bodies of 53 men who had been bound and blindfolded before they were shot to death in Baghdad -- apparently the latest victims of sectarian death squads.
"We firmly believe that national reconciliation is the only guaranteed path toward security, stability and prosperity. The alternative, God forbid, is death and destruction and the loss of Iraq," Prime Minister Nouri al-Maliki said in his opening remarks.
The gathering was touted by the Iraqi government and the White House as a chance to rally ethnic, religious and political groups around a common strategy for ending the country's violence.
Iraq's politicians, however, have been unable to unite and the Shiite prime minister faces growing dissent by coalition partners, including Shiite allies like radical cleric Muqtada al-Sadr.
Al-Sadr's bloc said it was boycotting the two-day meeting, as did two major Sunni groups and former Prime Minister Ayad Allawi, a secular Shiite.
Al-Sadr's absence came amid recent reports that some rival lawmakers are trying to sideline the anti-U.S. cleric, whose Mahdi Army militia has been blamed for some of the worst sectarian violence.
Al-Maliki imposed few conditions on the return of former military personnel to the army, only cautioning that those who serve in the new army should be loyal and professional.
The government had previously invited former officers up to the rank of major to join the new army. Al-Maliki's overtures were apparent concessions to a demand by Sunni Arab politicians who argue that the neglect of former soldiers was pushing them into the insurgency.
L. Paul Bremer, Iraq's former U.S. governor, dissolved Iraq's 400,000-strong army soon after American forces overthrew Saddam's regime in April 2003. The decision is widely seen as a mistake because it drove many into opposition.
On a visit to Iraq, U.S. Sen. John Kerry said Saturday that meeting with American and British troops helped clear his thoughts about what needs to be done to stabilize the country and he looked forward to hearing ideas from Iraqis. Kerry, the Democratic nominee for president in 2004 and possibly a future contender, had more meetings scheduled Sunday.