The United States has sent out a stark warning to Turkey over its plan to buy the advanced Russian-built S-400 air defense missile systems, stating that the purchase of the anti-aircraft platform will dramatically affect military ties between the two NATO allies.

AVA- Pentagon Spokesperson Eric Pahon told Turkey’s Ahval news agency in a written statement on Monday that the US understands Turkey’s desire to improve its air defense.
“However, Turkey’s acquisition of the Russian S-400 air defense system will have grave consequences for the US defense relationship with Turkey,” Pahon said.
The senior American defense official further noted that the United States is “working to help Turkey find better solutions to address its defense needs while also warning of the broader implications of purchasing Russian S-400s.”
Last week, acting Pentagon chief Pat Shanahan delivered a similar warning to Turkey, emphasizing that the purchase could result in Ankara’s exclusion from the program to build and operate F-35 advanced fighter jets.
“My position is that the S-400 and F-35 are incompatible – meaning that they don't go together,” Shanahan said in an interview with Bloomberg television news network last Thursday.
“We want to find a solution that makes the F-35, for a strategic partner, a critical asset in their military,” he said.
Washington has reportedly proposed to deliver one US-made Patriot missile system by the end of 2019, on the condition that Ankara abandons the deal with Moscow.
Two senior Turkish officials familiar with the talks, requesting anonymity, said on Friday that Turkey has rejected the offer as it didn't include a loan agreement nor a technology sharing pact.
Moscow and Ankara finalized an agreement on the delivery of the S-400 missile systems in December 2017.
Back in April last year, Turkish President Recep Tayyip Erdogan and his Russian counterpart Vladimir Putin said in Ankara that they had agreed to expedite the delivery of S-400 missile systems. At the time it was said that the delivery could be made between late 2019 and early 2020.
A number of the US-led North Atlantic Treaty Organization (NATO) member states have criticized Turkey for its planned purchase of S-400 missile defense systems from Russia, stating that the missile batteries are not compatible with those of the military alliance.
They also argue that the purchase could jeopardize Ankara's acquisition of F-35 fighter jets and possibly result in US sanctions.