The threat is to airlines that have direct flights to Russia, including some that originate in the United States, says a law enforcement official speaking on condition of anonymity because he was not authorized to discuss details of the warning.
The department said in a statement that the U.S. "isn't aware of a specific threat to the homeland at this time."
The statement notes the department - quote - "regularly shares information with domestic and international partners, including those associated with international events such as the Sochi Olympics."
The warning comes on the eve of the Winter Olympics.
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