The FBI is investigating a letter that's reported to contain a terrorist threat.

Honolulu TV station KITV reports the letter to the bureau's office in Honolulu threatens an attack on a Navy base in Hawaii.

The FBI confirms it received a letter but won't discuss what was in it.

A spokesman says the letter originated from within the U.S. The Joint Terrorism Task Force is investigating.

The Honolulu television station reports it obtained an e-mail memo reportedly distributed to Navy commanders. It says the letter sent to the FBI claimed a large shipment of explosives would be delivered to Honolulu for an attack on a Navy base in December.