But the issue is much deeper: many see the S-400 deal as a first - and large - step toward Russian Federation and away from the West.
"As you may know, the S-400 is one of the most complicated systems consisting of a large set of technical components, so there are quite a few nuances".
A Turkish newspaper is quoting President Recep Tayyip Erdogan as saying that both Ankara and Moscow are committed to Turkey's purchase of S-400 missile defense systems from Russian Federation.
"The S-400 missile system deal has already been signed by officials".
Points of dispute also included the barring of Turkish politicians from holding campaign rallies in European Union countries ahead of last April's referendum, and concerns over the powers granted to Erdogan in the closely fought plebiscite.
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"Putin and myself are determined on this issue", he told journalists.
Erdogan defended sovereignty of Turkish in terms of military matters, ensuring that "we make decisions about our own independence, we are obliged to take security measures to defend our country".
The voice of criticism rose from the United States after Erdoğan announced the decision to purchase the S-400 air defense system in late July. "The Pentagon recently said the same thing, although in a tepid tone: "It's a good idea" for allies to buy interoperable equipment".
Western governments have expressed concern over the deal - which Erdogan said in July had been signed - as it can not be integrated into the North Atlantic Treaty Organisation system.
Ankara objected to the criticism by the USA, underlining that another North Atlantic Treaty Organisation member state, Greece, formerly purchased the Russian S-300 defense system and has been using it for years.