(CNN) -- A United Airlines flight originating in Denver, Colorado, was diverted to Salt Lake International Airport in Utah on Thursday after a threatening letter was found on board, airport public relations director Barbara Gann told CNN.
Passengers were being held in the airport's international terminal while the plane is inspected, Gann said.
The incident was not affecting other flights.
United Airlines Flight 741, a Boeing 757, was en route to San Francisco, California, CNN affiliate KSL reported.
The FBI, ATF, Salt Lake City Fire Department and bomb-sniffing dogs responded to the scene, KSL reported.

In the immortal words of Joe Stack 'desperate times require desperate measures' I imagine many more will arrive at this conclusion in our near future. We have only been discussing and predicting this for at least the last five years. Maybe we should all apply for a job with the FBI's B.A.U. Oops! my bad, they believe in analysis after the fact don't they? I for one will be avoiding Federal Buildings and large gatherings. Its interesting the way Joe tried to express solidarity with Blacks and other Minority immigrants in his manifesto; there is one glaring difference however, Blacks and minority immigrants do not possess that inherently 'White' sense of entitlement, they are more likely to blame God, themselves and their choices for any failures.