Law enforcement and fire officials were investigating a potential threat on a plane at Denver International Airport on Monday afternoon, but police later said the threat was unfounded.Frontier Airlines said crewmembers discovered what they described as "threatening notes" on a plane.

Passengers slid down an emergency slide of a smoking jet at Denver's airport due to a possible problem with the plane's landing gear, authorities said.

One of the passengers was taken to a hospital with a minor injury, American Airlines said in its statement.