Frontier crew members discovered two threatening notes on a flight headed from Seattle-Tacoma International Airport to Denver, according to the airline.

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.

Denver police Monday afternoon confirmed passengers on a flight arriving to Denver International Airport were evacuated due to a threat that "appears to be unfounded at this time."