Russia and Turkey are preparing a contract for the delivery of a new batch of Russian S-400 missile systems, Interfax news agency cited a senior official at a Russian military cooperation agency as saying on Friday.
Such a deal would be likely to further strain Ankara's relations with Washington, which has suspended Turkey from the U.S. F-35 stealth fighter jet program, in which it was a producer and buyer, to penalize it for buying S-400 batteries this year.
"We're gradually working on this question. Most importantly, both sides are intent on continuing cooperation in this sphere," the head of Russia's Federal Service for Military-Technical Cooperation was quoted as saying.
The official, Dmitry Shugaev, said he thought there was a "fairly high likelihood" Turkey and Russia would sign a contract for the delivery of an additional batch of S-400s next year.
The head of Russia's state arms exporter told RIA news agency on Nov. 26 that Moscow and Ankara were actively discussing Ankara taking up an option in its original missile contract for it to receive more S-400 systems.
However, a U.S. defense official said Wednesday that the country will continue to try to persuade Turkey to give up the S-400s.
Under Secretary of Defense for Policy John Rood said Washington will engage in dialogue with Ankara to solve the matter.
The S-400 system has been a sticking point between Turkey and the U.S. for some time. Washington has argued that it would be incompatible with NATO systems and would expose its advanced fifth-generation F-35 jets to possible Russian subterfuge.
Turkey, however, has rejected calls to back out of the deal, emphasizing that the S-400 would not be integrated into NATO systems and would, therefore, pose no threat to the alliance.
Ankara also pointed out that the U.S. decision against selling Patriots led Turkey to seek out other sellers, adding that Russia offered it a better deal, including technology transfers.
Turkey even proposed setting up a commission to clarify any technical issues, but the U.S. has so far not responded to the proposal.
The acquisition of the Russian system prompted U.S. President Donald Trump's administration to remove Turkey from the F-35 Joint Strike Fighter program in July. Ankara was formerly a major buyer and manufacturer in the program.
Tensions deepened in the following months, especially after Turkey received its first shipment of the Russian equipment. Washington warned it would impose sanctions beyond removing Turkey from the F-35 program.
The Ankara-Moscow S-400 deal was inked in December 2017, when the parties signed a $2.5 billion agreement for two batteries of the S-400, which is Russia's most advanced long-range anti-aircraft missile system, in use since 2007.