The incident happened on Monday at 0500GMT (8am), an US military statement said. No further details were provided.
More than 1000 members of the US military have died since American-led forces invaded Iraq in March 2003.
Meanwhile, a South Korean air transport contingent is headed for Kuwait to support Korean troops deployed in a Kurdish province of northern Iraq, the South Korean defence ministry said.
The 150-member contingent along with four C-130H planes left a military airport south of Seoul to be based in a US airport base in Kuwait from Tuesday, the ministry said.
The air force unit is to airlift supplies and personnel for South Korean soldiers stationed in Iraq, it said.
The South Korean contingent is
South Korea deployed about 2800 troops for a relief and rehabilitation mission to Arbil, a Kurdish-controlled town in northern Iraq, last month.
They will be reinforced by another 800 soldiers in November.
The South Korean contingent is the third largest of the US-led forces in Iraq.