The grudging admission came on Thursday as US senators investigated disclosures of sexual and psychological abuse of detainees at the Abu Ghraib prison near Baghdad.
During a Senate Armed Services Committee hearing, Democrats confronted Deputy Defence Secretary Paul Wolfowitz and General Peter Race, the number-two official at the Pentagon, with "rules of interrogation" approved by the top commander in Iraq, Lt.Gen Ricardo Sanchez.
Those methods included sleep and sensory deprivation, forcing prisoners to assume "stressful" body positions for up to 45 minutes, threatening them with guard dogs, keeping them isolated for longer than 30 days and dietary manipulation.
Senator Jack Reed asked Pace if a foreign nation held a US Marine in a cell, naked with a bag over his head, squatting with his arms uplifted for 45 minutes, whether would that be a good interrogation technique or a Geneva Convention violation.
"I would describe it as a violation, sir," replied Pace, vice-chairman of the Joint Chiefs of Staff.
"As I read General Sanchez's guidance, precisely that behaviour could have been employed in Iraq," Reed pointed out.
Reed then asked Wolfowitz a similar question. Wolfowitz initially tried to sidestep it, but eventually replied, "What you have described to me sounds, to me, like a violation of the Geneva Convention."
US interrogation techniques have come under scrutiny amid revelations prisoners were kept naked, stacked on top of one another, forced to engage in sex acts and photographed in humiliating poses.
Human rights activists have said the US interrogation methods clearly violated the Geneva Convention.