American Airlines on Tuesday grounded all its flights in the US due to an unspecified technical issue, according to the company and a notice on the Federal Aviation Administration website.

Shares of the carrier were down 3.8 percent before the bell.

"An estimated timeframe has not been provided, but they're trying to fix it in the shortest possible time," the company said in a post on X, responding to a question from a stranded flyer.

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The US Federal Aviation Administration was not immediately available for further comment.