KABUL • Pressure is growing for an international inquiry into a United States strike on a hospital in Afghanistan, after the military detailed "tragic but avoidable" errors while refusing to say if there would be an independent investigation.

Doctors Without Borders (MSF) slammed US forces for "gross negligence" on Wednesday after the US commander in Afghanistan said the Oct 3 strike on a charity-run hospital in the northern city of Kunduz was "caused primarily by human error".

The raid killed 30 and forced the charity to close the trauma centre - the only one in the region - while stirring global condemnation.

General John Campbell, speaking at Nato headquarters in Kabul on Wednesday, said the incident was "caused primarily by human error". He blamed, in part, fatigue of US troops who had been battling the Taleban for five days, adding that the mistake was "compounded by process and equipment failures".

Gen Campbell described how a gunship aircraft hit the hospital instead of a nearby Afghan intelligence compound thought to have been taken by the Taleban.

Those who requested and executed the strike "did not undertake appropriate measures to verify that the facility was a legitimate military target", he said.

The strike began at 2.08am local time, Gen Campbell said, and at 2.20am, MSF phoned the US military to report they were under attack. "It took the headquarters and the US special operations commander until 2.37am to realise the fatal mistake... The strike lasted for approximately 29 minutes."

The gunship's electronic systems had malfunctioned, he said, cutting off communications, and the aircraft had strayed from its path, degrading the accuracy of "certain target systems". Thus when the crew entered the coordinates, they were directed to a field 300m from the intended target.

"The air crew visually located the closest, largest building near the open field which we now know was the MSF trauma centre," Gen Campbell said. At night, the crew were "unable to identify any signs of the hospital's protected status".

"We have learnt from this terrible incident," he said.

Gen Campbell's spokesman, Brigadier-General Wilson Shoffner, would not say if the probe would be followed by an additional independent international probe, for which MSF has repeatedly called.

MSF general director Christopher Stokes said after the announcement: "The frightening catalogue of errors outlined today illustrates gross negligence on the part of US forces and violations of the rules of war."

He added that the probe left "more questions than answers" .

Gen Campbell said individuals involved in the attack had been suspended pending "standard military justice", but would not give details on who was responsible.

AGENCE FRANCE-PRESSE