A US military investigation says "human error" and technical failures were the cause of airstrike on a Médecins Sans Frontières hospital in northern Afghanistan last month, which killed 30 people.

At least 13 staff and 10 patients, along with several unidentified victims, were among the dead at the complex in Kunduz on October 3, in an attack which the NGO described as a war crime.

US General John Campbell said a military investigation found the incident "was the direct result of human error compounded by systems and procedural failures."

He said US forces involved did not know the target compound was the MSF trauma centre, and "believed they were striking a different building several hundred metres away, where there were reports of enemy combatants."

The hospital had been targeted based on a visual description given by Afghan forces.

"Tragically this misidentification continued throughout the remainder of the operation, even though there were some contradictory indicators," said Campbell.

Bombing continued on the hospital 30 minutes after MSF had notified American and Afghan military officials in Kabul and Washington. The NGO had also provided precise GPS coordinates for their facilities to parties in the region as recently as September 29.

Initially the US military said it had come under fire from the complex before the attack, but later admitted fault and launched an investigation.

MSF has previously demanded that a full and independent investigation be established into the attack.

“Under the clear presumption that a war crime has been committed, MSF demands that a full and transparent investigation into the event be conducted by an independent international body, said Christopher Stokes, General Director, Médecins Sans Frontières.

"Relying only on an internal investigation by a party to the conflict would be wholly insufficient."