"The Secretary’s spoken to it, and we have said that the S-400 defence system, the acquisition of that would have serious consequences for the United States and NATO’s defence relationship with Turkey", Ortagus said. "We’re clearly willing to engage with them and have continued to engage regarding our concerns on this acquisition, but there will be very real and very negative consequences if that happens".
NBC News reported earlier in the day that Turkey has until June to abandon the deal with Russia, or Ankara will face US sanctions for importing Russian military technology.
Turkey has repeatedly rejected calls for cancelling S-400 shipments, saying it is a done deal. Kremlin spokesman Dmitry Peskov responded to the US ultimatum to Ankara on Wednesday by calling it unacceptable.
The United States earlier threatened Turkey with sanctions for its planned acquisition of S-400s and repeatedly said it may delay or cancel the sales of F-35 aircraft to Ankara. Turkey is one of seven states that participate in the F-35 program.
Ankara has said that the purchase of defensive weapons is its sovereign affair and has ruled out the possibility of abandoning plans to complete the purchase.