US Vice-President Mike Pence has warned Turkey against buying a Russian S-400 anti-aircraft missile system that Washington sees as a threat to US jets.
He said Turkey “must choose” between remaining a key Nato member or risk the security of that partnership “by making such reckless decisions”.
Turkey responded that the purchase of the advanced system was a done deal.
Ankara has been establishing closer links with Russia after recent souring of its ties with the US and Europe.
Mr Pence also rebuked Germany – another key Nato member – for not spending enough on its defence.
Turkish Foreign Minister Mevlut Cavusoglu repeated that the deal with Russia – thought to be worth about £2.5bn (£1.9bn) – would not be cancelled.
In a tweet, Turkey’s vice-president later wrote: “The United States must choose.
“Does it want to remain Turkey’s ally or risk our friendship by joining forces with terrorists to undermine its Nato ally’s defence against its enemies?”
The S-400 “Triumf” is one of the most sophisticated surface-to-air missile systems in the world.
It has a range of 400km (250 miles) and one S-400 integrated system can shoot down up to 80 targets simultaneously.
