Two fighter jets were sent to shadow a US plane yesterday after a "kissing" couple locked themselves in the toilet for a long time.

The Mile High pair raised fears about possible suspicious behaviour onboard the domestic flight from Denver to Detroit as US airspace was on heightened alert due to the 10th anniversary of the 9/11 attacks. 

When the plane landed, it was met by SWAT police and searched. Two men and a woman were escorted off the plane, but no charges were made.

Passenger Belinda Duggan, of Michigan, said: “All of a sudden, a SWAT team went through and saying, please place your hands on the seat in front of you.”

FBI Detroit spokeswoman Sandra Berchtold said: "Due to the anniversary of September 11, all precautions were taken, and any slight inconsistency was taken seriously. The public would rather us err on the side of caution than not.”