The KLM Royal Dutch Airlines said on Sunday that its flight from Amsterdam to Mexico City was approaching the US border from Canada on Friday when it was told it would not be allowed into US airspace because it deemed two people on board to be a security risk.

KLM spokesman Bart Koster said the plane returned to Amsterdam and resumed its Mexico City flight as normal on Saturday without the two passengers, whose names were not released.

It was not known what happened to the two passengers singled out by US authorities.

Koster said Dutch authorities did not consider them to be suspects, and they were not on any European no-fly lists, describing the incident as unique because US and European no-fly lists are usually the same.

"I guess they went their way," he added.