REUTERS/Medecins Sans Frontieres
"This deeply shocking event should be promptly, thoroughly and independently investigated and the results should be made public," Zeid Ra'ad al-Hussein said in a statement.
"The seriousness of the incident is underlined by the fact that, if established as deliberate in a court of law, an airstrike on a hospital may amount to a war crime."
Since the Taliban seized Kunduz six days ago, their biggest land grab in 14 years, the Afghan government has used US air power to bomb the area. The MSF said it was most likely US-led forces that bombed the hospital on Saturday.
"All indications currently point to the bombing being carried out by international Coalition forces," MSF said in a statement.
"MSF demands a full and transparent account from the Coalition regarding its aerial bombing activities over Kunduz on Saturday morning."