A police bomb squad is searching a plane that took off in San Francisco this afternoon and was diverted to Phoenix, a Phoenix police sergeant said.

United Express Flight 5573 left San Francisco International Airport at about 3 p.m. today and was originally bound for San Antonio but was diverted to Phoenix Sky Harbor International Airport at about 4:45 because of an unspecified threat, according to airport and airline officials.

All passengers safely got off the plane, according to United Airlines spokeswoman Mary Clark.

The aircraft was been isolated on the northwest side of the Phoenix airport while Phoenix police investigate the threat, airport spokeswoman Julie Rodriguez said.

The plane’s passengers and luggage are being re-screened in the airport, Phoenix police Sgt. Steve Martos said. A bomb squad is searching the plane but so far investigators have found nothing to corroborate the threat.

Martos said he could not elaborate on the nature of the threat and that the investigation will ultimately be handled by the FBI.

FBI officials were not immediately available for comment.

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