The aid agency Medecins Sans Frontieres (MSF) is seeking to invoke a never-used body to investigate the American bombing of its hospital in the Afghan city of Kunduz on Saturday.
The International Humanitarian Fact-Finding Commission (IHFFC) was set up in 1991 under the Geneva Conventions. The medical charity's president, Joanne Liu, said the bombing, which killed 10 patients and 12 staff, was an attack on the very conventions meant to govern the conduct of war.
MSF said the warring sides were well aware of the hospital's location in Kunduz, and that the bombing went on for a more than an hour despite repeated calls to United States and Afghan military officials in Washington and Kabul to call off the strikes.
The United States said the attack was a mistake and it was attempting to strike the Taliban. The president, Barack Obama, has telephoned Ms Liu to apologise personally.
White House spokesperson Josh Earnest said he could not say legally whether the bombing was a war crime but the US "goes to great lengths to limit the loss of life" of civilians.
In a statement, MSF said it had received the apology but was still demanding the IHFFC investigate. It said the coordinates of the hospital were well known and its bombing could not have been a mistake.
The commander of the American military in Afghanistan, General John Campbell, admitted "the decision to provide aerial fires was a US decision, made within the US chain of command".
He told a Senate committee in Washington that the hospital was "mistakenly struck" and promised a "thorough, objective and transparent" investigation.
A number of inquiries have been ordered, by the US justice department, the Pentagon, Nato and an American-Afghan team, but MSF has said it would not trust internal military inquiries into the bombing.
The US military has changed its account of how the air strike came about. Statements initially said US forces had come under fire, but then said air strikes were requested by Afghan forces under Taliban fire.
The Afghan defence ministry said "armed terrorists" were using the hospital "as a position to target Afghan forces and civilians".
MSF has denied this: "Not a single member of our staff reported any fighting inside the hospital compound prior to the US air strike on Saturday morning."
Mr Obama has also apologised to the president of Afghanistan.
"If it is necessary to hold individuals accountable, that will be done," White House spokesperson Josh Earnest said.
Mr Earnest also hinted at the possibility of paying victims and their families, a Department of Defense policy.
Can the commission investigate?
MSF said statements from the Afghan and US forces implied they worked together to deliberately target the hospital, which amounts to an admission of a war crime.
Ms Liu said the International Humanitarian Fact-Finding Commission was "the only permanent body set up specifically to investigate violations of international humanitarian law", and she called on the commission's signatory states to activate an inquiry.
However, according to the IHFFC provisions, an inquiry needs the specific endorsement of the parties to the conflict.
Neither the US nor Afghanistan is a signatory, and therefore they would have to issue separate declarations of consent to the investigation of the Kunduz bombing.