"Our only concern about it is one of interoperability… but it is a Turkish decision," Davis told reporters.
The Russia-Turkey talks on the delivery of S-400 systems have taken place since 2016. In March, Sergei Chemezov, CEO of Russia’s Rostec Corporation, said Ankara was ready to buy the systems with a loan granted by Moscow. On July 18, Chemezov said technical issues of the contract for the supply of the S-400 systems to Turkey had been resolved, with only administrative ones remaining.
On Friday, Turkish presidential spokesman Ibrahim Kalin said only few nominal issues are left to clear up in a generally formalized contract on the delivery of Russia's S-400s to Turkey.
Turkish President Recep Tayyip Erdogan said last week that Ankara and Moscow had signed a document on supplies of the S-400 Triumf systems.