U.N. prosecutors said on Thursday they had evidence suggesting international forces in Afghanistan had caused serious harm to detainees by subjecting them to physical and psychological abuse.
The International Criminal Court (ICC) has been investigating alleged crimes committed since 2003 by all parties to the conflict in Afghanistan, but in previous reports on the status of its inquiry it has been far more circumspect about alleged crimes and the harm caused.
In its latest report on the many preliminary examinations it has open, the court's Office of the Prosecutor said U.S. investigations of alleged crimes by its soldiers had not yielded convictions or risen high up the chain of command.
The determination marks a significant escalation of the court's long-running investigation and could prove controversial in the U.S., which is not a member of the court and has in the past opposed it vociferously.
"The infliction of 'enhanced interrogation' techniques ... would have caused serious physical and psychological injury," prosecutors wrote.
They also noted that there was evidence of violations committed by Taliban and forces that supported the Afghan government, adding that neither appeared to be seriously investigating allegations against its own side.
Up to 37,000 civilian casualties had been attributed to anti-government forces since 2007, and pro-government forces appeared to have meted out "gruesome" treatment to some 5,000 detainees, prosecutors said.
They were still trying to determine the gravity and scale of any violations committed by international and U.S. forces, they said.
All NATO members contributed to the International Security Assistance Force mission to Afghanistan that ran from 2001 until last year. Forces from the U.S. and other countries remain in the country on a NATO training exercise.