US air marshals have detained a diplomat amid claims he tried to set his shoes on fire on board a United Airlines flight from Washington.
The alarm was reportedly raised when an air marshal smelled smoke in the cabin of flight 663, hald an hour before the aircraft was due to land.
The marshal confronted a man who had spent an extended period of time in the bathroom and claimed he was trying to set his shoes on fire.
Mohammed al-Modadi, a vice consul at the Qatari embassy in Washington, was arrested after the plane landed at Denver International Airport in Colorado.
But it remains unclear whether the passenger was joking or if anything was actually set on fire.
No trace of explosives
There were no reports of an explosion on the plane, and bomb-sniffing dogs are reported to have found no traces of explosives aboard the aircraft.
F-16 fighter jets were scrambled to escort the plane, which had taken off from Reagan Airport in Washington, in to land following the security alert.
The plane, carrying 157 passengers and six crew, landed safely at Denver International Airport, and was surrounded by emergency vehicles.
"Shortly before landing in Denver, a passenger possibly caused a disturbance on the plane," said a spokesman for North American Aerospace Defense Command (NORAD).
"Upon intercepting the aircraft, the F-16s escorted the aircraft until it landed safely without incident at approximately 6:50 pm (0050 GMT) where the plane was met by local law enforcement."
F-16 fighter jet escort
The Transportation Security Administration (TSA) said it was "monitoring" the incident "after receiving initial reports that a federal air marshal responded to a passenger possibly causing a disturbance on board this aircraft."
The security agency said "all steps are being taken to ensure the safety of the travelling public."
Mr al-Modadi has full diplomatic immunity thanks to his job as the third secretary and vice-consul of the Qatari embassy in Washington.
The latest incident came a week after the US unveiled new security measures subjecting all US-bound plane passengers to screening methods that use real-time intelligence to target potential threats, replacing the mandatory screening of passengers from a blacklist of 14 mainly Muslim countries that had angered some allies.
The measures were announced in the wake of a Nigerian man's failed attempt to detonate explosives concealed in his underwear on a Detroit-bound flight from Amsterdam on Christmas Day.