The Federal Aviation Administration briefly grounded flights in and out of Dallas' two main airports on Wednesday after a report of smoke in a radar room prompted an evacuation of the air traffic controllers, the agency said.

The ground stop applied to both Dallas-Fort Worth International Airport, a hub for American Airlines, and Dallas Love Field, a Southwest Airlines hub.

The facility affected by the report of smoke is not an air traffic control tower but a radar room where controllers monitor airspace over a large swath of north Texas.

Local firefighters had cleared the smoke in the facility and the FAA lifted the ground stop after that, said agency spokesman Lynn Lunsford.

"The controllers are back on position and the airspace is back to full capacity. It will likely take some time to work through the delays. Please contact the airlines for specific flight information," said Lunsford.

American Airlines said 28 of its flights were diverted because of the issue.

"Operations are now returning to normal. We apologize to our customers for the inconvenience and are working to rebook and re-accommodate customers as quickly as we can," the airline said in a statement.

DFW was the 12th busiest airport in the world, according to a 2017 ranking by Airports Council International, serving some 67 million passengers that year.