Three separate investigations -- by the US military, NATO and Afghan officials -- are currently under way into Saturday's catastrophic strike in the northern Afghan city of Kunduz.
But the charity, which condemned the attack as a war crime, stressed the need for an international inquiry, saying the bombing raid that killed 22 people was in contravention of the Geneva Conventions.
"We cannot rely on an internal military investigation," Doctors Without Borders (MSF) chief Joanne Liu told reporters in Geneva, insisting that an "international humanitarian fact-finding commission" should probe the bombing.
Saturday's raid sparked international outrage, fuelled by claims that patients had burned to death as they lay in their beds.
Liu's remarks come a day after General John Campbell, the top US and NATO commander in Afghanistan, said the "hospital was mistakenly struck" when Afghan officials called for the raid.
But MSF brushed aside that explanation, saying "a mistake is not an answer for us" and insisting on knowing "the facts, the intention, the criteria" behind the more than hour-long raid.
International aid groups, the United Nations and a growing tide of global revulsion have added to the pressure on Washington to come clean over the strike, which came days after the Taliban overran Kunduz.
The New York Times on Tuesday, citing officials close to Campbell, said US special forces in Kunduz were unable to verify whether the hospital was a legitimate target before the bombs were dropped.
But the official stressed that no final conclusions had been reached and a formal inquiry could yield a different conclusion.
