Reports alleging that the delivery of Russian S-400 surface-to-air missile defense systems to Turkey are delayed are not true, and the delivery period is continuing as planned, Turkish Foreign Ministry Spokesperson Hami Aksoy said Friday.

Stating that reports claiming that Ankara was considering a delay in the procurement of the systems upon Washington's request were not a reflection of reality, Aksoy reiterated that Turkey's offer to the U.S. to form a joint working group to address concerns about the systems still stands.

The United States and Turkey have been at loggerheads over Ankara's decision to purchase the S-400s from Russia. Washington has warned that proceeding with the deal could result in U.S. sanctions and the exclusion of Turkey from the F-35 fighter jet program.

The U.S. is still trying to dissuade Turkey from purchasing the Russian-made missiles, but Ankara has on a number of occasions voiced its determination to go through with the deal.

In due consideration of regional and global developments that pose grave risks to its national security, Turkey decided to meet its need for an air defense system from Russia and inked a $2.5-billion deal with Moscow in December 2017, after the U.S. repetitively rejected selling Patriot missiles to Turkey.

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.

In the face of U.S. claims, Turkey proposed setting up a working group to address the technical concerns on the S-400 system, but the U.S. has not yet responded to Turkey's offer.

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