Few nominal issues are left to clear up in a generally formalized contract on the delivery of Russia's S-400 missile systems to Turkey, Turkish presidential spokesman Ibrahim Kalin said Friday, Sputnik News reports.

Turkish President Recep Tayyip Erdogan said this week that Ankara and Moscow had signed a document on supplies of the S-400 Triumf systems.

"The negotiations are coming to an end. This I can clearly state. Minor points relating to the agreement remain to be clarified. However, in general terms, the agreement has already taken shape," Kalin said as quoted by Turkey's Anadolu news service.

Earlier, Ankara's ambassador to Moscow, Huseyin Dirioz announced that Turkey's membership to NATO does not impede the supply of Russia's S-400 air defense missile systems to the country.

Turkey has agreed to pay Russia 2.5 billion dollars for Russia's S-400 missile systems.