An envoy from Qatar who authorities said grabbed a surreptitious smoke in a US jetliner's bathroom and then joked about lighting his shoe on fire was released from custody after sparking a bomb scare and a widespread securiy alert.

Jet fighters were scrambled to intercept the Washington-to-Denver flight, but no explosives were found.

Authorities said they don't think the envoy was trying to hurt anyone during Wednesday's scare and he will not be criminally charged.

"This diplomat was traveling to Denver on official embassy business on my instructions, and he was certainly not engaged in any threatening activity," Qatar's US ambassador, Ali bin Fahad Al Hajri, said. "The facts will reveal that this was a mistake."

Brown Lloyd James, a law firm representing the Qatar embassy, said that the diplomat, Mohammed Al Madadi, had been released by authorities after questioning and was on his way back to Washington. The firm said Al Madadi is the embassy's third secretary.