A helicopter has gone down north of the Iraqi capital Baghdad killing two US troops, the US military has confirmed.
The US did not say what caused the crash but witnesses said the helicopter was shot down, near a US air base at Taji, shortly after dawn.
Another helicopter was hit by gunfire but managed to fly away, they said.
Last month, 12 US soldiers died when a Black Hawk military helicopter crashed. The US has lost more than 50 military helicopters in Iraq since May 2003.
Officially the Pentagon did not say what sort of helicopter had crashed or how, but a US defence official anonymously told the AFP news agency that it was a US Army AH-64 Apache and that "the initial report is that it was a shoot-down".
Iraqi police and witnesses told the Associated Press that the crash occurred about 0730 (0430 GMT) as two Apaches were flying near Taji, a major US base about 20km (12 miles) north of Baghdad.
While one escaped the other flew back to attack the source of the gunfire, but was hit, exploded and fell to earth.
Separately the US military said it had killed 18 insurgents in the Sunni flashpoint town of Ramadi in western Iraq.
It said US forces killed the insurgents over two days after troops there came under fire.
Meanwhile Iraq authorities have declared a curfew in the Shia city of Najaf amid an upsurge of violence in the area.
Seventy-three people were killed and 167 injured in a double suicide bombing in nearby Hilla on Thursday.
Also, some 263 people were killed in clashes with US-backed Iraqi troops near Najaf earlier this week.