Baghdad (CNN) -- Five U.S. servicemembers were killed Monday in central Iraq, the U.S. military said in a written statement.
The deaths are the single largest loss of life among U.S. troops in Iraq since 2009, and they come as Iraq debates whether to request U.S. troops stay beyond a January 1, 2012, deadline that requires 46,000 American forces out of the country.
The U.S. military did not say how or where the five died.
But two Iraqi security officials told CNN Monday that the servicemembers were killed during an early morning mortar attack at a U.S. military base in southeastern Baghdad.
Five servicemembers also were wounded in the attack, said the officials, who spoke on condition of anonymity because they were not authorized to release the information.
The two officials said some of those killed and wounded were sleeping in trailers when the base was attacked.
U.S. Army Sgt. First Class Anishka J. Calder, a spokeswoman in Baghdad, declined to comment on details surrounding the deaths.
The names of the servicemembers were being withheld pending notification of next of kin, the military said in the statement.
The deaths follow warnings by the U.S. military that attacks against American troops in Iraq by armed militias are on the rise, an attempt to demonstrate their power ahead of an anticipated U.S. withdrawal at the end of the year.
U.S. troops have increasingly been targeted by roadside bombings and mortar attacks, largely in Baghdad and southern Iraq, Army Maj. Gen. Jeffrey S. Buchanan, spokesman for U.S. Forces-Iraq, recently told CNN.
While al Qaeda in Iraq -- predominantly Iraqi Sunni insurgents -- continue to launch strikes, Buchanan has said the militia attacks against the United States are "designed for power and they want to claim credit for our redeploying, for us leaving."
Meanwhile Monday, 20 Iraqis were killed in a series of explosions across the country. The deadliest attack was in Tikrit, where a suicide bomber rammed a vehicle packed with explosives into a security checkpoint staffed by Iraqi army and police, killing 11 people and wounding 17 others, according to Interior Ministry officials who declined to be identified because they were not authorized to speak to the media. Most of the casualties were Iraqi security forces, Interior Ministry officials told CNN.