A U.S. security official said, "It may have been a massive misunderstanding" and the diplomat's statement may have been a "sarcastic" comment when he was confronted by two air marshals who had been told by flight attendants that smoke was coming from the lavatory.
Law enforcement authorities in Denver say the air marshals and the diplomat were in a "physical confrontation."
The suspect was identified by authorities as a diplomat in the Qatar embassy in Washington, Mohammed al Modadi, 27. The FBI said the man had full diplomat immunity as the 3rd secretary and vice-consul.
The plane was taken to a remote location after landing at Denver and passengers were questioned by FBI agents about the incident. A bomb squad team and explosives-sniffing dogs were still on board the plane late Wednesday night.
Authorities said White House officials had been briefed on the incident as it unfolded.