President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Thursday expressed his displeasure with the release of John Walker Lindh, the man known as the "American Taliban," saying he will be "watching him closely."

"Am I happy about it? Not even a little bit," Trump said when fielding questions during a White House event to announce aid for farmers affected by a trade dispute.

The president said he went to government lawyers recently and asked what could be done when he heard Lindh was due to be released.

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"I went and checked, and he said, 'From a legal standpoint there is nothing we’re allowed to do, because if there was, I would have done it instantly,'" Trump said.

"But we'll be watching him. We'll be watching him closely," he added. "What bothers me more than anything else is here's a man who has not given up his proclamation of terror. And we have to let him out."

Lindh, 38, was released on Thursday after serving 17 years of a 20-year prison sentence.

The California native left home at age 17 to study in Yemen. He traveled to Pakistan in 2000 and later served as a Taliban volunteer at a training camp in Afghanistan.

Lindh encountered U.S. troops just weeks after the 9/11 terror attacks. He pleaded guilty in 2002 to aiding the Taliban and carrying weapons, cooperating with prosecutors in a deal that prevented details of his alleged mistreatment by U.S. forces from being released, CNN reported.