Turkey on Friday received its first shipment of S-400 missile defense system hardware from Russian Federation, the nation's defense ministry said.
US officials have encouraged Turkey to buy the Patriot missile defense system instead of the S-400s.
The move will anger the United States, which has warned that Turkey can not have both the S-400 anti-aircraft defence system and US F-35 fighter jets.
US officials are anxious the Turkey-Russia deal could give the Kremlin access to crucial intelligence shared between Washington. and Turkey and compromise North Atlantic Treaty Organisation developments.
Nick Heras, of the Center for a New American Security, said the S-400 system would be a "game changer" for Turkey's air defence strategy in a region surrounded by actors with well-developed air forces.
Turkey and the U.S. are North Atlantic Treaty Organisation allies - but Turkey has also been establishing closer links with Russian Federation.
Fears over a fresh bout of sanctions also saw Turkey's dollar-denominated sovereign bonds tumble sharply and the price of insuring exposure to government debt spike.
President Tayyip Erdogan said after meeting President Donald Trump at a G-20 summit last month that the US did not plan to impose sanctions on Ankara for buying the S-400s.
The mounting diplomatic pressure is seeing Turkey push back, saying it will not bow to worldwide pressure and as a sovereign nation, it has the right to buy whatever it wants from any country.
A Russian transport jet Friday brought the first delivery of the $2.2 billion missile system to a Turkish military air base outside Ankara, causing concern from Brussels to Washington.
Kremlin spokesman Dmitry Peskov told journalists on Friday that "everything is happening in strict accordance with the agreements and signed contracts, all obligations are being carried out". The Russian Ministry of Defense tweeted footage of the plane carrying the S-400s touching down in Turkey.
"The S-400 is incompatible with the F-35", Lord said June 7.
The detention of US consular staff in Turkey has also strained relations, along with disagreements over Iran, Venezuela and Middle East policy.
On Friday, a North Atlantic Treaty Organisation official told The Washington Post that the alliance was "concerned about the potential consequences of Turkey's decision to acquire the S-400 system". But Turkey says the offer does not meet its requirements, including possible future joint production.
On Friday, Akar said, however, that Turkey was also considering purchasing the American system.
It's a Russian-made, long-range, surface-to-air defense system. Earlier this month, U.S. Senator Lindsey Graham appeared to raise the bar for sanctions, saying they may be triggered only when the missile system is activated.
Russia's Federal Service for Military-Technical Cooperation confirmed it had started delivering the S-400 to Turkey and that the deliveries would continue as per an agreed schedule, the RIA news agency reported.
Despite the issues, Luke still accepted the third and fourth F-35 jets for the Turkish pilot training program at the 63rd Fighter Squadron in April. "Planting that air-defense system on Turkish soil could, by means of its powerful radar, help Moscow discover the secrets - and the vulnerabilities - of the F-35s that Turkey intends to acquire".