U.S. President Barack Obama has said the Pentagon has launched a "full investigation" into air strikes that killed at least 22 people at an Afghan hospital.
Nearly 40 other people were seriously injured in the October 3 strikes on the hospital run by Doctors Without Borders (MSF) in the northern city of Kunduz.
MSF said on October 4 that 12 staff members and 10 patients, including three children, had died in the attack.
Offering his "deepest condolences" over the attack, Obama said he expected a "full accounting of the facts" and would then make a definitive judgement.
UN rights chief Zeid Ra'ad Al-Hussein said that "if established as deliberate in a court of law, an air strike on a hospital may amount to a war crime."
"This event is utterly tragic, inexcusable, and possibly even criminal," he added.
MSF said its hospital was partially destroyed after being hit by a sustained "aerial attack" amid ongoing fighting between the Taliban and NATO-backed Afghan government troops to gain control of Kunduz.
"We are deeply shocked by the attack, the killing of our staff and patients, and the heavy toll it has inflicted on health care in Kunduz," MSF said.
The charity also said that it had provided the GPS coordinates to coalition and Afghan military and civilian officials as early as September 29.
“All indications currently point to the bombing being carried out by international coalition forces,” MSF said in a statement posted online.
"U.S. forces conducted an air strike in Kunduz city at 2:15 a.m. ... against individuals threatening the force. The strike may have resulted in collateral damage to a nearby medical facility. This incident is under investigation," NATO said.
The U.S. Embassy in Kabul voiced sympathy for the victims in the bombing and "all those suffering from the violence in Kunduz."
Afghan Interior Ministry spokesman Sediq Sediqqi said 10 to 15 "terrorists" had been hiding in the hospital at the time of the strike.
Afghan President Ashraf Ghani’s office issued a statement earlier saying the commander of NATO’s Resolute Support Mission had apologized to Ghani over the hospital bombing. NATO, however, said it was not aware of such an apology.
MSF said that, at the time of the bombing, the hospital had 105 patients and their caretakers and more than 80 international and Afghan staff were present.
MSF said it had treated 394 people wounded in fighting since the Taliban attacked the city on September 28.
Government forces largely regained control over the strategic city of 300,000 on October 1, but sporadic fighting continues as Afghan troops track down remaining Taliban fighters.
During the fighting, the U.S. military launched several air strikes to support government forces.
Taliban spokesman Zabihullah Mujahid issued a statement saying there were no Taliban fighters in the hospital at the time of the bombing. It blamed Afghanistan's intelligence service for misdirecting the air strike to purposefully hit the hospital.
The MSF clinic in Kunduz comprises several buildings and is located in the east of the city, not far from the local office of NDS, the Afghan intelligence service.