ANKARA, Turkey — Turkish and Russian government officials are in an “advanced stage of negotiations” to finalize a potential deal on Russian-made Su-35 fighter aircraft, Turkish officials said.

“The talks have quite matured,” a senior Turkish procurement official told Defense News on the condition of anonymity. “A deal does not appear to be too distant.”

If penned, an Su-35 deal will be Turkey’s second major purchase of weapons systems from Russia. Unnerving its NATO allies, Turkey acquired the Russian-made S-400 long-range air defense system. The S-400s were delivered to the Turkish military in August.

The Turkish official said that although the final numbers may change during the negotiating process, Turkey could buy two squadrons (a batch of 48) Su-35s.

An aerospace industry specialist in Ankara said Moscow would probably price the fighter aircraft between $50 million and $70 million. “The potential Su-35 deal has strategic value for the Russians,” he said.

“Moscow may thus agree to give Ankara a favorable price reminiscent of the S-400 deal,” he added. Turkey agreed to pay $2.5 billion for two S-400 systems. The contract came with an international loan.

After Turkey finalized its S-400 deal with Russia, the U.S. suspended Turkey’s partnership in the American-led, multinational Joint Strike Fighter consortium that builds the F-35 Lightening II fighter jet.

Meanwhile, Turkey is struggling to design and develop its first indigenous fighter jet. Turkish officials originally hoped to fly the “national fighter jet” in 2023, but industry sources say this is an unrealistic target.

A government official said any Su-35 deal would be an off-the-shelf purchase. “All the same, we would expect our Russian partners to assist our fighter jet program with some technology transfer,” he said.