Doctors Without Borders said that an international commission has been formed to investigate the U.S. bombing of its hospital in Kunduz, Afghanistan, this month that killed 22 people.
The medical charity, also known by its French acronym MSF, said the Swiss-based International Humanitarian Fact-Finding Commission had been activated at the request of a state that it did not name.
"This is the first step needed to undertake an independent investigation into the attack," MSF said in a statement.
It said the commission was awaiting a final agreement from Afghanistan and the United States to proceed.
President Barack Obama has apologized to the head of MSF. "There was a mistake and it's one that the U.S. owns up to," White House spokesman Josh Earnest said last week. He said Obama "is very eager to get to the bottom of what exactly occurred."
MSF said it could not rely on internal investigations by parties to the conflict.
"We have received apologies and condolences, but that is not enough," said MSF International President Joanna Liu. "We are still in the dark about why a well-known hospital full of patients and medical staff was repeatedly bombarded for more than an hour. We need to understand what happened and why."
The top U.S. commander in Afghanistan, Army General John Campbell, said the United States was taking the blame for carrying out the October 3 raid after Afghan forces requested it to attack Taliban insurgents it believed were firing from inside the medical facility. But the question remains whether the U.S. should have agreed to the attack.