"Two US service members were killed in central Iraq Sunday night," a statement from the US military said.

"This was one incident resulting in the death of two US service members. These are the first deaths of any US service member in 2011," a spokeswoman for the military said, without giving further details on how the two were killed, or to which branch of the military they belonged.

Some 50,000 US troops remain in the country, but a security accord between Baghdad and Washington requires that they be withdrawn by the end of 2011.