Doctors Without Borders/Médecins Sans Frontières (MSF) on Wednesday are waiting for a response from the U.S. and Afghanistan to approve a formal investigation into the bombing of its charity hospital earlier this month.

MSF announced that a formal request has been made to the International Humanitarian Fact-Finding Commission (IHFFC) to investigate the U.S. military airstrike in Kunduz, Afghanistan, marking the first time the Commission has been activated since its inception in 1991 under the Geneva Conventions.

"The IHFFC stands ready to undertake an investigation but can only do so based on the consent of the concerned State or States," the commission wrote in a statement Wednesday.

It is unclear if the U.S. or Afghanistan will give permission for the investigation to move forward. MSF has consistently said it cannot rely on internal investigations by the U.S. Department of Defense, Afghan officials, or the North Atlantic Treaty Organization (NATO), which are currently underway, and previously called on both governments to allow for an independent probe of the October 3 bombing that killed 22 people, including patients and staff.

President Barack Obama made a formal apology to the medical charity and the Pentagon has said it plans to give "condolence payments" to victims' families, but MSF international president Dr. Joanne Liu has maintained that the organization's biggest priority is an impartial inquiry into the airstrike.

"We have received apologies and condolences, but this is not enough. 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," Liu said Wednesday. "We need to understand what happened and why."

"We need to know if the rules of war have changed, not just for Kunduz, but for the safety of our teams working in frontline hospitals all over the world," Liu said.