The helicopter came down on Wednesday in al-Haditha district near the western flashpoint town of Ramadi after hitting an electrical cable over the river Euphrates, Aljazeera's correspondent reported.
The OH-58 Kiowa helicopter crashed into the water at 1:50pm (10:50 GMT), a US military spokesman confirmed.
"The site is secured and we can confirm two people killed," he told AFP new agency. He did not know how many were on board.
The Kiowa, a military observation and reconnaissance helicopter, normally carries a crew of two, however.
It is the second such incident in a month. On 25 January, an OH-58 Kiowa Warrior helicopter crashed into the Tigris in the northern city of Mosul, where police said the aircraft had flown at low altitude into cables strung across the river.
It was the fifth crash last month involving a US military helicopter in Iraq, most caused by hostile fire.
In the worst incident on 9 January, a UH-60 Black Hawk aircraft was shot down near the hotspot of Falluja, west of Baghdad, killing all nine people on board.