UPDATE (9:15 p.m. ET):United reports the ground stop has been lifted.
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Computer problems briefly grounded all domestic United Airlines flights in the United States on Sunday night.
SEE ALSO: Flying give you 'the fear?' Here are the world's safest airlinesA posting on the FAA's Air Traffic Control command center website confirmed the issue, with the ground stop listed as applying to all domestic airports in the lower 48 states.

Meanwhile, travelers noticed the stoppage and United acknowledged that they were working to remedy the situation.
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As for this writing, flights were already backed up at major United hubs like Denver, Chicago O'Hare, and Houston.
Mashablehas reached out to United Airlines for comment on the issue.
This is a developing story...
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