John Walker Lindh, the American captured in Afghanistan in 2001 fighting for the Taliban, was freed early from federal prison on Thursday after serving 17 years amid concerns he might still harbor extremist views.

U.S. President Donald Trump told reporters at the White House that he had asked government lawyers whether the release could be stopped but said nothing could be done.

"What bothers me more than anything else is that here's a man who has not given up his proclamation of terror, and we have to let him out. Am I happy about it? Not even a little bit," Trump said.