A NATO official told CNN on Friday: "It is up to allies to decide what military equipment they buy. However, we are concerned about the potential consequences of Turkey's decision to acquire the S-400 system." Those consequences are shaking the alliance given Turkish media is already reporting a punitive response from Washington is imminent:

U.S. sources tell Ahval, there will be a response by the U.S. government with regards to the arrival of S-400 Russian defense systems in Turkey, soon.

Russia's TASS news has indicated a second delivery will be made in the coming weeks, with a third delivery, carrying over "120 anti-aircraft missiles of various types" to be delivered "tentatively at the end of the summer, by sea."

TASS also noted that Turkish S-400 operators will receive training on the systems in Russia, following a prior training program involving 20 Turkish personnel last Spring.