OTTAWA (AFP) - A United Airlines flight from Alaska to Denver was diverted to Vancouver after a "security concern" and one person was placed in custody on Saturday, officials said.

Airline and airport officials would not immediately say what the problem was, but the incident came as the United States and Canada are on heightened alert for terror attacks.

"United Airlines flight 1104 from Anchorage, Alaska to Denver, Colorado was diverted to Vancouver International Airport due to a security concern," an airport spokeswoman said.

"The Royal Canadian Mounted Police are responding."

Richmond Royal Canadian Mounted Police subsequently tweeted: "We have a suspect in custody. Airport operations unaffected at this time. More information when available."

The plane landed safely and the airline is cooperating with authorities, United said.