Denver International Airport evacuated a section of its main terminal on Tuesday as officials investigated a possible security threat, airport officials said on Twitter.
"DPD is evacuating a section of the main terminal on the west side between doors 600 and 610 to investigate a possible security threat," tweet sent by the Denver Airport said.
The evacuation area included the west side of the main terminal levels 5 and 6, the airport said. Flights continued while the possible threat was investigated.
"No vehicle traffic is being allowed on the west side of the terminal. East side remains open to passengers," another tweet by the airport said.
An airport spokesman told AFP that police were evacuating the western side of the terminal but that flights were continuing.
"It's a possible physical threat," Heath Montgomery said, without elaborating.
"Vehicle traffic has been stopped on the west side of the terminal, however, passengers may continue to access the east side of the terminal."
Montgomery said that several airlines had ticket counters inside the area evacuated -- including American Airlines, Aero Mexico, Lufthansa and British Airways -- and flight delays were possible.
Heightened security was put in place at major U.S. airports following attacks in Brussels earlier in the day.