The issue of Turkey, a US NATO ally, buying Russian air defence systems has been straining relations between Washington and Ankara since December 2017, when the deal with Moscow was inked. The US claims that the Russian systems pose a threat to American F-35 jets Ankara is also willing to buy. This reported by Sputnik.

The US has requested Turkey delay the procurement of Russian S-400 systems, slated to take place this July, to 2020 in a bid to win some tome to convince Ankara to scrap the deal with Moscow, Bloomberg reported, citing two anonymous sources. According to the media outlet, Turkey is currently considering the American request, but hasn't responded yet.

Russia is unaware of Turkey's plans to delay the delivery of the S-400s, Kremlin spokesman Dmitry Peskov told the media. The issue wasn't raised during either of the last telephone conversations between the Russian and Turkish presidents.

The news comes amid talks about a possible visit by US President Donald Trump to Ankara in July. The two states' relations have spiralled downward since Turkey inked a contract with Russia on the procurement of S-400 defence systems in December 2017. The deal was signed after Ankara failed to get the air defences it wanted from the US on suitable terms, Erdogan explained later.

US officials insist that not only will the S-400 be incompatible with NATO's air defence grid, but it also allegedly poses a threat to America's top jet, the F-35, which Turkey helps build and wants to procure for itself. Washington has reportedly halted the delivery of the jets Ankara's already ordered, citing concerns the S-400 may reveal its weaknesses to Moscow. The US also considered imposing sanctions on Turkey in connection with S-400 deal.