North Atlantic Treaty Organisation member Turkey's move to acquire the S-400s has been regarded in some Western capitals as a snub to the alliance amid tensions with Russian Federation over its role in the wars in Syria and eastern Ukraine.
Turkey's President Recep Tayyip Erdogan said talks have been held with Russian Federation on the S-500 system.
His Foreign Minister Mevlut Cavusoglu was quoted on Monday as saying North Atlantic Treaty Organisation member Turkey could seek a deal to acquire a missile defence system with another country if Russian Federation does not agree to joint production of the defence shield.
Earlier in an interview with The Washington Post, US permanent representative to North Atlantic Treaty Organisation called Turkey's decision to purchase Russian S-400 "Triumph" missile system a "big problem".
"In our talks with (Russia President Vladimir) Putin we are not thinking of stopping with the S-400s".
The S-400 deal, announced last month, has also caused concern because the Russian-made weapons can not be integrated into the alliance's defenses.
The S-500 missile system, developed by Russian manufacturer Almaz-Antey, will enter service in the coming years, the Russian Defense Ministry said earlier this year.
However, NATO Secretary-General Jens Stoltenberg said this week Turkey was not seeking to antagonise the USA -led alliance by purchasing the system and is in talks with France and Italy to buy similar weapons.