The Transportation Security Administration (TSA) says that it "is aware of an alleged threat made via phone against American Airlines Flight 24 (SFO-JFK) before take-off."
All passengers are safe and out of an abundance of caution, TSA requested the plane be moved to a remote location. Passengers are being deplaned and will be interviewed and rescreened. The aircraft will be swept by local law enforcement.
According to the San Francisco Chronicle, "the nature of the threat was not disclosed."
There were 163 passengers and 11 crew members on the plane, The Associated Press reports, citing American Airlines spokesman Tim Smith.