A US investigation into a strike on an Afghan hospital run by a charity cited mistakes so "reckless" that observers said they left open the unsettling question of whether those involved had ripped up their own rule book in a chaotic effort to take out the Taliban.

The Oct 3 strike on a Doctors Without Borders hospital in Kunduz was "primarily human error ... compounded by systems and procedural failures", said General John Campbell, the US commander in Afghanistan, as he announced the results of the investigation this week.

The strike came after a resurgent Taliban briefly captured the northern provincial capital in their biggest military victory since they were toppled in 2001.