A rocket-propelled grenade hit the Russian-built Mi-8 helicopter as it flew over a deserted area north of Baghdad, Reuters reported, citing Bulgarian officials and the U.S. military.
The six Americans killed were employed by Blackwater Security Consulting, a subsidiary of North Carolina-based security contractor Blackwater USA. They were assisting the Bureau of Diplomatic Security in protecting U.S. diplomats in Iraq.
The chartered flight appears to be the first civilian aircraft shot down since the U.S.-led invasion of Iraq two years ago.
A militant group called the Islamic Army in Iraq claimed responsibility for shooting down the helicopter, and posted a video on the Internet showing insurgents shooting the crash's sole survivor, international news agencies reported on 21 April.
"One of the crew members was captured alive and killed," the Islamic Army in Iraq said in a statement posted on its website. The video showed what appeared to be the burning remains of the helicopter and a man in blue overalls lying in a grassy area and reaching out for help, Reuters reported.
"Give me a hand," he was heard saying. Insurgents helped the man get up, ordered him to walk away and shot him repeatedly while shouting "Allahu Akbar," or God is Great.