Fallujah killing could be war crime: HR groups

"If it is what it appears to be, then obviously it would be a grave breach of the Geneva Conventions. It would probably be a war crime," said Joe Stork, Washington director of the Middle East division of Human Rights Watch.

Human Rights Watch and Amnesty International echoed calls by the top U.N. human rights official, Louise Arbour, for an investigation of suspected abuses in Fallujah, Iraq, including the disproportionate use of force and targeting of civilians.

The US military has launched an investigation after NBC pool footage showed a US Marine shooting a wounded and unarmed man in a mosque in Falluja, the scene of fierce fighting in the past week.

NBC said the Marine had been shot in the face the day before, and his fellow soldiers have spoken out in his defence, saying he was under combat stress in unpredictable, dangerous circumstances.

Amnesty International spokesman Alistair Hodgett said investigations into other incidents in Iraq had been too slow and he urged a prompt, open, inquiry, after which findings should be made public.

"The deliberate shooting of unarmed and wounded fighters who pose no immediate threat is a war crime under international law and there is therefore an obligation on the US authorities to investigate all such reports and to hold perpetrators of such crimes accountable before the law," said Amnesty.