WASHINGTON - United Airlines said it had grounded its flights at US airports on Wednesday due to a technology issue, and warned of additional flight delays in the evening.

"Due to a technology issue, we are holding United mainline flights at their departure airports," the airline said.

United suffered an outage of its weight calculation system, a source familiar with the matter told Reuters.

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"The issue affecting United Airlines flights has been resolved and mainline flights are departing once again," flight tracking website FlightRadar24 said on social media at 9:19 pm ET (0119 GMT on Thursday).

The US Federal Aviation Administration said earlier it issued a ground stop for United flights at several US airports.

The ground stops were issued at major United hub airports including Newark, Denver, Houston, Chicago, according to the regulator's website.

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As of 9:25 pm ET, flight tracking data from FlightAware showed that 870, or 28 percent, of United flights had been delayed on Wednesday.

United's outage came a few weeks after Alaska Airlines grounded all of its flights for about three hours due to an IT outage for the second time in just over a year.

In April 2024, Alaska grounded its entire fleet due to an issue with the system that calculates the weight and balance of its planes.