14 September, 2017
He stressed that the purchase of weapons from a non-NATO country, referring to Russian Federation, is not consistent with the principles of the alliance, and said "NATO's joint missile defense system remains the best option to defend Turkey from all threats in its region".
Erdogan said Monday that Turkey had already paid a deposit for two batteries of the advanced missile systems.
Russian Federation says that S-400 missiles are created to protect vital political, economic, administrative and military facilities from airstrikes, and are considered of the most advanced systems in the air- and anti-missiles defense.
"They have gone insane because we made a deal for S-400s".
"What are we supposed to do? I expect tensions to ease", Cemil Ertem, Erdogan's chief economic adviser, said in an interview on Tuesday.
Western governments have expressed concern over the deal - which Erdogan said was finalised in July - as it can not be integrated into the North Atlantic Treaty Organisation system.
Some media reports have said the deal could be worth up to $US2.5 billion.
Turkey faced similar worries during the Iran-Iraq War and the First and Second Gulf Wars due to the ballistic missiles possessed by those countries.
He said Turkey would continue to take "important steps" to ensure its security.
His explanations, however, did not stop the outpouring of criticism from the USA and other members of the military alliance.
The S-400 is Russia's next-generation air defense system, carrying three different types of missiles capable of destroying aerial targets at a short-to-extremely-long range.
Turkey has been developing stronger ties with Russian Federation and souring on its relationship with the United States, which has supported the YPG Syrian Kurdish rebels during the Syrian civil war, the BBC News reported.
The Turkish president has also slammed American officials for rejecting his requests to hand over Fetullah Gulen, a powerful opposition figure living in the US.
The minister went on to say that Germany's decision to put arms deals with Turkey on hold would only make Turkey stronger and help it develop its defense industry.
The spat has prompted Germany to restrict its arms sales to Turkey.