Russian Foreign Minister Sergey Lavrov yesterday criticized the U.S. for trying to pressure prospective buyers of Russian weapons, including Turkey.

The growing centers of influence will not bow to "ultimatums and threats" when deciding what and where to buy, Lavrov said in a speech at a youth forum.

Countries "will not agree to subjecting their right to trade with who they want and what they want to ultimatums and threats, as is now the case with contracts for the supply of Russian weapons to a number of states, for example, Turkey, Indonesia and India, when Washington openly requires refusal of these contracts," he said. Lavrov also warned that such U.S. demands would create "unpredictability, and an additional potential for conflict."

On June 18, the U.S. Congress passed legislation to ban the sale of F-35 fighter jets to Turkey, despite a signed contract between the two countries.

Turkish President Recep Tayyip Erdoğan later said that U.S. President Trump had assured him that the sale was not in question, despite the congressional effort.

Russian President Vladimir Putin also previously said U.S. pressure on Turkey over the purchase of the S-400 air-defense systems will not produce any results.

Recently, U.S. Secretary of Defense Jim Mattis warned the U.S. Congress to not ban the sale of F-35 fighter jets to Turkey. U.S. lawmakers were seeking to do so in response to Turkey's decision to buy S-400s from Russia. U.S. Defense Secretary is expected to prepare an extensive report on Turkish-American relations and Turkey's role in the F-35 program.

In December, Turkey officially signed a $2.5 billion agreement with Russia for the S-400s, Russia's most advanced long-range anti-aircraft missile system. With the move, Turkey is set to become the first NATO member country to acquire the system.

With the S-400s, Ankara aims to build Turkey's first long-range air and anti-missile defense system to boost its defense capabilities amid threats from PKK and Daesh terrorists at home and conflicts across its borders in Syria and Iraq.

Moreover, Turkey seeks to build its own missile defense systems as the deal also involves the transfer of technology and know-how. The S-400 system, which was introduced in 2007, is the new generation of Russian missile systems, and so far Russia has only sold them to China and India. The first batch of S-400 is expected to be delivered in early 2020.