All of United Airlines flights were grounded Sunday because of a computer outage, the Federal Aviation Administration said.

"A ground stop is in place for domestic flights due to an IT issue," United tweeted. "We're working on a resolution. We apologize for the inconvenience."

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The ground stop was lifted after 9 p.m.

"The ground stop has been lifted," United tweeted. "We're working to get flights on their way."

The Aircraft Communications Addressing and Reporting System, or ACARS, was having issues with low bandwidth, officials told NBC News.

International flights were not affected.

This is a developing story. Check back for updates.

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Atlanta art and antiques appraiser and auctioneer Allan Baitcher (right) takes bids during a 2020 auction. Baitcher and his company, Peachtree Antiques, are being sued by a Florida multimillionaire who says he paid them $20 million for fakes. (AJC 2020)

Credit: Phil Skinner / Staff