WASHINGTON—The deadly attack earlier this month at a U.S. consulate in Libya was "deliberate and organized," the top U.S. spy's office said Friday.

The revised assessment by the Director of National Intelligence, the office that heads up the various U.S. spy agencies including the Central Intelligence Agency, is the most declarative U.S. statement yet that the Sept. 11 assault on U.S. diplomatic sites in Benghazi, Libya—which left four Americans dead, including U.S. Ambassador Christopher Stevens—was a coordinated terrorist...