The strike Saturday on the hospital run by Doctors Without Borders (MSF) in the northern Afghan city killed 22 people, sparking international outrage in an incident the medical charity branded a war crime.
US special forces on the ground in Kunduz were unable to verify whether the hospital was a legitimate target before the bombs were dropped, a New York Times report said Tuesday, citing officials close to General John Campbell.
But the official stressed that no final conclusions had been reached and a formal inquiry could yield a different conclusion.
Under the rules of engagement, airstrikes are called in to eliminate insurgents, protect American troops and assist Afghans who request air support.
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But the US special forces most likely did not meet any of that criteria, Campbell said in private discussions with his colleagues, according to the report.
The general stressed that while it was the Afghans who called for the strike, ultimately the decision to launch rested with Americans.
He said US officials were communicating with the charity, also known by its French name Medecins Sans Frontieres (MSF), to get "all sides of the story".
Three separate investigations into the strike are underway.
The remarks came as Campbell urged Washington to consider boosting its post-2016 military presence to repel a Taliban upsurge and stabilise a "tenuous security situation" in the war-ravaged nation.