The four deaths occurred during combat in Diyala province, an area northeast of Baghdad that continues to be volatile despite an overall drop in violence nationwide.
The attack came two weeks after a suicide car bomber struck a U.S. patrol in the northern Iraqi city of Mosul, killing four American soldiers and an Iraqi interpreter in the deadliest single attack against U.S. forces in nine months.
At least 4,250 members of the U.S. military who have died in the Iraq war since it began in March 2003, according to an Associated Press count.
The statement did not provide more details about the attack or identify those killed pending notification of relatives.
President Barack Obama, who campaigned on a promise to end the war in Iraq, is expected to announce further troop withdrawals in the coming weeks after his recent announcement that he is sending thousands more combat forces to Afghanistan.
Iraq's Interior Ministry, meanwhile, announced the arrest of a Shiite police gang accused of killing the Sunni vice president's sister in 2006 as part of a string of kidnappings and slayings.
Spokesman Maj. Gen. Abdul-Karim Khalaf said the 12 people arrested were former employees of the ministry. The Interior Ministry has been accused of past infiltration by Shiite militias who carried out some of the worst sectarian violence.
The sister of Vice President Tariq al-Hashemi, Maysoun al-Hashemi, died in a hail of gunfire on April 27, 2006 as she left her home in Baghdad.
Abdul-Karim al-Samarraie, a member of al-Hashemi's Iraqi Islamic Party, welcomed the arrests.
"It is a good thing that Interior Ministry succeeded in arresting Maysoun al-Hashemi's killers ... although it took to long to find them," he said.
In the most recent violence, gunmen ambushed an Iraqi army checkpoint Monday in western Baghdad, killing three soldiers and wounding eight other people, according to police.
Also Monday, a roadside bombing apparently targeting a police patrol in central Baghdad killed at least two civilians and wounded six, said police and hospital officials.
The officials spoke on condition of anonymity because they weren't authorized to release the information.