The video was issued by the Islamic State in Iraq, an umbrella group of Iraqi fighter groups.
US denial
James Conway, US marines commandant-general, said his forces did not believe that the CH-46 Sea Knight helicopter, the Marine-version of the Chinook, was shot down.
Your Views

"Success for Iraq  will need both groups coming to terms and to work together for the benefit of all Iraqis"

Iceman, Atlanta, US

Send us your views

US military officials said early indications were that the craft's loss was due to mechanical failure.
The Islamic State in Iraq issued a written claim of responsibility on Wednesday for the craft's downing and had promised a video would follow.
The video, entitled "the Hell of Christians and Apostates in Iraq", was posted on a web forum where fighter groups often post messages.
Its authenticity could not be independently confirmed.
Attacks increasing
The crash was the sixth by a US helicopter since January 20, at least four of them downed by ground fire.
An Iraqi air force officer on Wednesday also said the CH-46 had been shot down. Five marines and two navy medics were killed in the crash.
Though he said the CH-46 was not believed to have been shot down, Conway said on Wednesday that there was a new and troubling "intensity of effort" by fighters to attack helicopters.