A Qatari man who caused a security scare on a United Airlines flight was a diplomat travelling on official business and posed no threat, the Qatar News Agency said on Thursday.

The incident prompted security officials to scramble two F-16 fighter jets to intercept the  aircraft and escort it to Denver International Airport. "We respect the need for special security measures for air-related travel...but the diplomat was traveling to Denver on official duty related to the embassy," Ali bin Fahad Al-Hajri, Qatar's ambassador to Washington, said in a statement to QNA. 

The statement did not name the diplomat.   

But it said: "He certainly wasn't involved in any activities involving a threat. This was a mistake and we request that all parties concerned refrain from making any assumptions or judgements." 

Earlier report said the Qatari man sparked a security alert after he was apparently caught smoking in the toilet and made a remark that was perceived as a threat.

US officials said he was in custody and the incident did not appear to be serious.

Coming just months after the failed "underwear" bomb attempt on Christmas Day, the scare prompted security officials to scramble two F-16 fighter jets to intercept the Boeing 757 aircraft and escort it to Denver International Airport where it landed at about 9 pm. EDT (0100 GMT on Thursday) .

"It looks like the individual in question was perhaps smoking in the lavatory and might have made an unfortunate remark" when confronted by airline personnel, a US official said.

President Barack Obama was briefed on the disturbance and a White House official said "actions were taken to ensure the safety of the traveling public."  But passengers aboard United Airlines flight 663 said there was no struggle and that the suspect appeared to be speaking calmly to a US air marshal in first class.

"I didn't know anything had happened until we landed," said Tim Burney, a first class passenger sitting one row in front of the man who was handcuffed and taken away for questioning at Denver International Airport.

Burney said he overheard the marshal telling the man "just be honest with me" and the passenger saying something about being "embarrassed."    

US officials have been on heightened alert and have ramped up security substantially since Christmas Day last year after a Nigerian man tried but failed to blow up a flight from Amsterdam to Detroit with a bomb hidden in his underwear.

The first reports of Wednesday's incident heightened security at other airports, such as Los Angeles Airport, where police said they added patrols. 

ABC News, citing federal law enforcement officials, first reported that air marshals subdued a Qatari man who authorities say tried to "light his shoes on fire" on the flight, sparking fears of another attack.   

CNN said no explosives were found on board and identified the man as a mid-level Qatari diplomat. When asked why he was in the toilet so long, he "said something about lighting his shoe on fire," the network reported. 

US officials could not confirm that report, while officials at the Qatari Embassy in Washington could not be reached. "Law enforcement and TSA have responded to the scene and the passenger is currently in custody," the Transportation Security Administration said in a statement.   

There were 157 passengers aboard the plane and six crew members, according to United Air. - Reuters