DENVER -- A passenger on a flight from Washington, D.C., to DIA reportedly made a comment that he was trying to light his shoes on fire during the flight.

Federal air marshals on the flight stopped and restrained the man, who was a first class passenger on United flight 663 from Reagan National Airport to DIA Wednesday night. United flight 663, a Boeing 757, landed in Denver at 6:50 p.m.

The man, identified as Mohammed al-Madadi, a diplomat in the Qatar embassy in Washington may have been smoking in the bathroom. The FBI said the man had full diplomat immunity as the 3rd secretary and vice-consul.

Two law enforcement officials said investigators were told the man was asked about the smell of smoke in the bathroom and he made a joke that he had been trying to light his shoes -- an apparent reference to the 2001 so-called "shoe bomber" Richard Reid.

The sources asked not to be identified because they were not authorized to discuss the ongoing investigation.

On Christmas Day, a Nigerian passenger on flight bound for Detroit from Amsterdam tried to ignite an explosive device.

Bomb squad crews have been seen coming and going from DIA. ABC News reported that no explosives have been found on the airplane.

During 7NEWS' breaking news coverage, we mistakenly showed video of a United airplane being towed into a hangar, and identified that plane as United flight 663. That plane was not flight 663.

Call7 Investigators confirmed that the White House was alerted to and monitored the incident on the plane. The Palm Beach airport tower in Florida confirmed with the Call7 Investigators that pilots in the air were warned with the following alert:

"All pilots be advised, a U.S. air carrier pilot reported a passenger that his shoes on fire. Any similar incidents must be reported to ATC (air traffic control) immediately."

Denver International Airport has remained open during the incident. There has been no impact on flight operations, and there are no flight delays or cancellations.

There were 157 passengers and six crew members on the flight. They were taken to a nearby fire station where they were questioned about the incident on the plane.

7NEWS reporter Dayle Cedars is at DIA and spoke with Jayne Smith, the wife of flight 663 passenger Scott Smith. Jayne relayed to Cedars that a first class passenger had some sort of a "temper-tantrum" on the flight.

TSA released this statement:

“TSA is monitoring an incident on board United Airlines flight 663 from DCA (Reagan) to DEN (DIA) after receiving initial reported that a Federal Air Marshal responded to a passenger possibly causing a disturbance on board this aircraft. The flight landed safely at Denver International Airport."

Two F-16 fighters, under the direction of North American Aerospace Defense Command (NORAD), intercepted the flight at approximately 6:45 p.m. Upon intercepting the aircraft, the F-16s escorted the aircraft until it landed safely without incident at approximately 6:50 p.m. where the plane was met by local law enforcement.

"Law enforcement and TSA have responded to the scene and the passenger is currently in custody. All steps are being taken to ensure the safety of the traveling public," said NORAD in a statement.

According to the AP, officials insisted Wednesday night it was still too early to tell whether the incident was an attempted act of terrorism or a giant misunderstanding.