Russia's stance on Turkey's purchase of its S-400 missile defense system has not changed, the country’s ambassador to Turkey said Wednesday.

Aleksei Yerkhov made the remarks at a reception in Ankara to mark Russian National Day.

Turkish Deputy Foreign Minister Sedat Onal along with several foreign diplomats attended the event at the Russian Embassy.

"There is no change and will be no change in the stance and position of the Russian Federation related to the S-400 [missile system]," Yerkhov told reporters.

Pointing to Russia's commitments to Turkey, Yerkhov stressed that it would fulfil its responsibilities.

Tensions between the U.S. and Turkey have reached a fever pitch in recent months with Turkey set to begin receiving the advanced S-400 Russian surface-to-air missile defense system which Washington has said will jeopardize Turkey's role in the U.S. F-35 fighter jet program and could trigger congressional sanctions.

Following protracted efforts to purchase an air defense system from the U.S. with no success, Ankara decided in 2017 to purchase the Russian S-400 system.

U.S. officials advised Turkey to buy the U.S. Patriot missile system rather than the S-400s from Moscow, arguing the Russian system would be incompatible with NATO systems and expose the F-35 to possible Russian subterfuge.

Turkey, however, emphasized that the S-400 would not be integrated into NATO systems and would not pose a threat to the alliance.

Yerkhov also spoke about the abolition of visas between Russia and Turkey.

"We are in constant contact with our Turkish colleagues about visas. But since the issue is a very detailed one, it would be too optimistic to think that it can be resolved in five minutes. I hope we will resolve it."

In February, Russian President Vladimir Putin signed a decree to lift visa requirements for Turkish service passport holders and truck drivers traveling to Russia.

The new rules are valid for Turkish citizens with special passports on short-term business trips, including to diplomatic missions and consular offices, as well as professional drivers transporting international cargo.