A security threat on board a United Airlines aircraft has led to a ground stop at Reagan National Airport outside Washington, D.C., two aviation sources tell NBC News.

Passengers were being offloaded from a United flight and bussed to the terminal, Reagan Airport said on social media.

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Flight operations are currently being held, the airport said.

“Departures to Ronald Reagan Washington National are grounded due to security,” a notice from the Federal Aviation Administration says.

Video shows a crowd of people leaving a United Airlines plane that landed at the airport.

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