President Trump said Thursday that he was very unhappy with the fact that "American Taliban" fighter John Walker Lindh was released early from prison.

"What bothers me more than anything else, is that here's a man that has not given up his proclamation of terror and we have to let him out," Trump said. "Am I happy about it? Not even a little bit. The lawyers have gone through it with a fine-tooth comb. If there was a way to break that, I would have broken it in two seconds. I knew about it very well."

Lindh was released two-and-a-half years before his 20-year sentence was set to end.

Trump also said he would have stopped Lindh’s early release if possible.

[ Related: Senators demand answers over early release of 'American Taliban' John Walker Lindh]

“Two weeks ago, I went to the best lawyers in our country that work for government. I said, ‘What can we do about this?’” the president said.

“I went and checked, and he said, from a legal standpoint, there’s nothing we're allowed to do,” Trump added. “Because if there was, I would have done it instantly. But we'll be watching him. We'll be watching him closely.”