MSF wants to invoke the International Humanitarian Fact-Finding Commission (IHFFC), a Switzerland-based international body, set up in 1991, which has never been called upon.

In a news briefing on Wednesday, MSF's president, Joanne Liu, said that "we cannot rely on an internal [US] military investigation" into a deadly US air strike on a hospital MSF was running in the Afghan city of Kunduz.

She said it was not just an "attack on our hospital - it was an attack on the Geneva Conventions. It can't be tolerated." Liu asked people to "stand with us to insist that even wars have rules."

The medical charity said that the Bern-based commission, which can be invoked at the request of a single state under the Geneva Convention, would gather facts and evidence from the United States, NATO and Afghanistan.

MSF would then decide whether to press criminal charges for loss of life and damage, Liu said.

"If we let this go, we are basically giving a blank check to any countries at war," she added.

On Tuesday, the US admitted that the deadly air strike was made within the "US chain of command" but said that it was "mistakenly struck."

At least 22 people died in the attack which the UN says could amount to a war crime. But it has also said it was too early for an independent probe.

ng/msh (Reuters, AFP)