(CNN) -- Two U.S. aircraft crashed in northern Iraq on Monday, killing four American soldiers, the U.S. military said.
The crash does not appear to be the result of enemy action, the U.S. military said, but it continues to investigate the case.
Police in Kirkuk said that the two craft crashed near the city.
Monday's crash appeared to be the worst for U.S. forces in Iraq since September, when 11 U.S. soldiers were killed in the crash of a CH-47 helicopter in southern Iraq. That crash was not believed to be the result of enemy fire either.
In November, two U.S. soldiers died when their OH-58 Kiowa helicopter crashed while on a mission over Mosul in northern Iraq.
Also Monday, a suicide car bomb killed a civilian and wounded an Iraqi soldier when it struck an army patrol, police in Mosul said.
CNN's Mohammed Tawfeeq and Jomana Karadsheh contributed to this report