A spokesman for United States Central Command said: "He was among the al-Qaeda and Taliban prisoners ... He is injured and is being given medical assistance by US forces."
The man, described as "a white, educated-sounding, apparently middle-class American", was taken into custody on Saturday at a hospital, where he had been admitted for treatment for minor gunshot and shrapnel wounds.
Mr Lindh, 20, spent his formative years in San Anselmo, a leafy suburb across the bay from San Francisco. He became Abdul Hamid when he converted to Islam at 16, a move grudgingly accepted by his parents.
"I was a student in Pakistan, studying Islam and came into contact with many people connected with Taliban," John Walker said in an interview shown on CNN television yesterday.
"I lived in the region, the North West Frontier Province (of Pakistan)," he said. "The people in general have a great love for the Taliban so I started to read some of the literature of the scholars, the history of Kabul ... my heart became attached to that."
"It isn't what they would have chosen for him," said a family friend, Bill Jones.
However John's father, Frank Lindh, who is divorced from his mother Marilyn, said that his son took to Islam naturally. "I support him and his studies," Lindh said. "He's learned Arabic and is memorising the Koran. He's a very good scholar."