Brigadier General Mark Kimmitt, the coalition's deputy director of operations, said on Sunday those arrested are "highly suspected of leading a cell that shot down a UH 60 Blackhawk helicopter on 15 November."

He didn't give further details.

The incident involved the collision of two Blackhawks killing 17 soldiers and the US military has so far said that the incident was under investigation, despite reports that they came under fire.

On Friday insurgents shot down a US military helicopter in the restive Iraqi town of Fallujah, killing one soldier and wounding another.

Kimmitt said US forces continued to detain four of five individuals who were posing as journalists and had pulled up to the site of the crash and started firing small arms and rocket-propelled grenades, before they were chased by US troops and four of them captured.

He said the incident remains under investigation.

Reuters news agency said Saturday that three of its employees arrested at the scene of the Fallujah helicopter crash were still in US custody and no reason had been given for their detention.