The dead included six Americans, two Fijian security guards, and two Bulgarian pilots and a Bulgarian engineer, said Paul Greenway, air operations manager for Toronto-base SkyLink.

Bulgarian officials earlier said the commercial helicopter was downed by a missile north of Baghdad and that the victims included three Bulgarians and two Filipinos.

A US security firm, Blackwater USA, said it had a deal with Skylink to operate the helicopter.

The Islamic Army in Iraq claimed the attack, releasing on the Internet a video showing what it said was wreckage of the stricken craft and the corpses of victims.

But Greenway said the incident was under investigation.

"Many people said the helicopter was shot down by a missile," Greenway said. "This is what was reported generally everywhere but in fact this is not necessarily the case. There is an inquiry going on. We don't know. We're not certain."