By Abhijith Ganapavaram and Utkarsh Shetti

(Reuters) -American Airlines ( AAL ) on Tuesday grounded all its flights in the U.S. due to an unspecified technical issue, according to the company and a regulatory notice, disrupting the travel plans of thousands of passengers set to fly out for Christmas Eve.

Massive flight stoppages have snarled the plans of numerous travelers in the past. Southwest Airlines experienced a systemwide meltdown in 2022 that lasted for days.

American has not provided a timetable for resolving the issue but was telling passengers on social media platform X to direct-message them to deal with ticketing issues and transfers.

"A technical issue is affecting American flights this morning. Our teams are working to resolve the issue as quickly as possible, and we apologize to our customers for the inconvenience," the company said in a statement to Reuters.

Numerous passengers were posting on social media that their flights had been stuck on the runway at various airports and were now being sent back to the gate.

American operates thousands of flights per day to more than 350 destinations in more than 60 countries.

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

The U.S. Federal Aviation Administration in a statement referred Reuters to the airline, reiterating that the carrier had reported a technical issue.

American was responding to comments on X as numerous users posted there, as well as on Bluesky and Facebook.

"Hey, @AmericanAir just tell us whether we should go home or not. Please don't make us wait in the airport for hours," wrote one user.

The grounding comes months after airlines were hit by a global tech outage tied to Microsoft's Azure cloud platform and a software issue at cybersecurity firm CrowdStrike.

The U.S. FAA was not immediately available for further comment.

Two years ago, Southwest Airlines experienced a meltdown with its systems during the holidays that led to 16,900 flight cancellations and stranded 2 million passengers. It was eventually fined $140 million in the largest-ever civil penalty for a travel disruption.

(Reporting by Utkarsh Shetti in Bengaluru; Editing by Shilpi Majumdar and Sriraj Kalluvila)