Turkey initially purchased the S-400 in 2017, plunging its relationship with the U.S. into crisis. As a result of the deal, the Trump administration expelled Turkey from the F-35 program and later sanctioned the country’s defense industry organization and its leaders. The United States fears the powerful S-400 radar system would allow Russia to spy on the advanced F-35 fighter jet.

But the reaction in the U.S. on Tuesday was comparatively muted. At a press briefing, State Department spokesman Ned Price urged Turkey not to further engage with Russia’s defense sector.

“The point that we have consistently made across the board is that Russia’s brutal and unjustified war against Ukraine makes it vital, now more than ever in some ways, that all countries avoid transactions with Russia’s defense sector,” he said.

“We’ll have to wait and see what happens, but we are not aware of any new developments on this matter,” Price added.

Price declined to address whether a new S-400 would prompt the Biden administration to reconsider plans to sell F-16 fighter jets to Turkey.

The Russian news agency TASS reported Tuesday Russia and Turkey have signed a contract for a second “regiment” of the S-400 to Turkey, quoting the head of the Federal Service for Military-Technical Cooperation, Dmitry Shugayev.

Turkish defense sources quickly rebutted Russian claims it had signed an additional contract, noting the second S-400 was part of the initial agreement.

Shugayev, the Russian official, reportedly told TASS the new agreement with Turkey will allow for some components of the system to be built in Turkey.

Turkish sources told Defense News there may be an agreement with Russia to domestically manufacture some S-400 components for the second regiment.

The Turkish Embassy in Washington didn’t return a request for comment.

Turkey’s complex balancing act between the West and Russia has only gotten trickier since Russia’s invasion of Ukraine. The strongest sign of a thaw between Turkey and the U.S. came in late June as Turkish leader Reccep Tayyip Erdogan dropped objections to Finland and Sweden joining NATO.

U.S. President Joe Biden then voiced support for the F-16 sale at the NATO summit in Madrid in June.

A delegation from Ankara arrived in the U.S. on Monday for the fourth round of technical talks with Washington on a potential F-16 deal, Turkey’s Anadolu Agency reported this week.

Turkey has asked to make a $6 billion purchase of 40 Lockheed Martin Block 70 F-16 fighter jets. It is also seeking a separate $400 million sale to upgrade their current F-16 jets with new missiles, radar and electronics.

Senate Foreign Relations Committee Chairman Bob Menendez, D-N.J., has threatened to block the F-16 sale over Turkey’s continued possession of the S-400s, its violations of Greek airspace and Cypriot waters in the eastern Mediterranean, its human rights record and ongoing attacks on U.S.-backed fighters in northeast Syria.

Menendez issued a statement on Thursday blasting reports that Turkey intends to proceed with the second S-400 batch and called on Ankara to “unequivocally demonstrate its commitment to NATO and to regional peace and security by fully rejecting any military cooperation with a war criminal like Vladimir Putin.”

“Between continued antagonistic violations of Greece’s airspace and the delaying of the accession process for Sweden and Finland’s NATO membership, I sincerely hope Turkey will change course and live up to its responsibilities to the defense alliance by being the constructive partner in the region we all hope it can be,” said Menendez. “The United States must be clear: Any expansion of Turkey’s ties to the Russian defense sector would be a grave mistake that would further endanger the security of our NATO allies and partners throughout Europe.”

Despite increased tensions with its NATO allies in recent years, Turkey has generated some goodwill in Washington over its support for Ukraine against Russia. Turkish firm Bayraktar has been selling Ukraine its TB2 laser-guided, bomb-dropping drone for use against Russian troops, and, in June, Ukraine said Bayraktar would open a drone factory within its borders to help repel the invasion.

In recent weeks, Erdogan also brokered an international deal with Russia to allow the export of grain from Ukraine, a breadbasket for the world, to ease a global food crisis. Agricultural goods had been stuck in Black Sea ports due to the invasion.

Eric Edelman, a former U.S. ambassador to Turkey and senior Pentagon official, said he believes the S-400 deal between “competimates” Erdogan and Russian President Vladimir Putin will confound efforts to mend ties between Turkey and the U.S.

“To say the least, this will complicate the Biden administration’s effort to sell F-16s to Turkey and enrage Turkey’s growing legion of detractors on Capitol Hill,” Edelman said.

Jim Townsend, the Pentagon’s top Europe and NATO policy official during the Obama administration, said he doubts the S-400 deal came about without Turkey giving advanced warning to the U.S. He hypothesized that it was a component of the international grain deal.

“This might be residue from that deal, and if that is the case, then we probably heard about it, not only because we were probably in the background of these discussions, but also so that the Turks don’t have to pay a price from the U.S. for doing something to make the grain deal work,” Townsend said.

The hushed U.S. reaction to the Russian report is a clue, he added.

“If we’re not thundering from the pulpit, we probably knew about it,” Townsend said.

Separately, the Turkish government congratulated Trump for his presidential victory while repeating its call for the extradition of US-based Islamic preacher Fethullah Gulen, accused of orchestrating the failed coup attempt of July 15.

Prime Minister Binali Yildirim said: “We congratulate Mr. Trump. I am openly calling on the new president from here about the urgent extradition of Fethullah Gulen, the mastermind, executor and perpetrator of the heinous July 15 coup attempt, who lives on US soil.” The prime minister said Gulen’s extradition could mark a new beginning in U.S.-Turkish relations.

“I am sure that the strategic partnership of Turkey and the US, which is based on a long history, has created an opportunity for the new president, paying attention to Turkey’s sensitivity in the fight against terrorism, carrying forward traditional friendly relations, [and] prioritizing peace and security in the region,” Yildirim added.

Turkey has been vehemently demanding Gulen’s extradition from the US since the failed putsch of July 15. Gulen, once a staunch political ally of Erdogan, has been living in self-exile in Pennsylvania since 1999.

Procurement officials in Ankara said the future of defense cooperation would largely depend on whether Trump would favour a policy for more technology transfers to Turkey.

“We do not think Trump’s election will be an immediate game-changer in procurement ties,” one official said. “Over time, however, we would expect him to pursue a policy to share more with NATO ally Turkey.”