TORONTO—In a video released Tuesday, a 16-year-old captured in Afghanistan cries out for his mother and says he needs treatment for his battle wounds during questioning by Canadian officials at the U.S. military prison in Guantanamo Bay. “Oh Mommy,” he cries in despair in Arabic when he is alone in the room, watched only by hidden cameras.

The 10 minutes of video provide the first glimpse of interrogations at the U.S. military prison. It shows Omar Khadr weeping, his face buried in his hands, as he is questioned by Canadian intelligence agents over four days in 2003. The lawyers hope to pressure Canada into seeking Khadr’s return, but the government said its position was unchanged.

The video, created by U.S. government agents at the prison in Cuba and originally marked as secret, provides insight into the effects of prolonged interrogation and detention on the Guantanamo prisoner.

A Canadian Security Intelligence Services agent in the video grills Khadr about events leading up to his capture as an enemy combatant when he was 15. Khadr, a Canadian citizen, is accused of throwing a grenade that killed one U.S. Special Forces soldier during a 2002 firefight in Afghanistan that left another soldier blinded. He was arrested after he was found in the rubble of a bombed-out compound—badly wounded and near death.

At one point in the interrogation, Khadr pulls off his orange prisoner shirt and shows the wounds he sustained in the firefight. He complains he cannot move his arms and says he had not received proper medical attention, despite requests.