A Lockheed Martin F-35 aircraft is seen at the ILA Air Show in Berlin, Germany, April 25, 2018. REUTERS/Axel Schmidt

The Trump administration has reaffirmed its opposition to Turkey’s rejoining the F-35 Joint Strike Fighter program, citing Ankara’s possession of Russian S-400 missile defense systems.

In a letter sent on Wednesday to US Rep. Chris Pappas (D-NH), a senior State Department official reiterated that Washington remains committed to enforcing the Countering America’s Adversaries Through Sanctions Act (CAATSA), which penalizes countries with financial ties to Russia’s defense sector.

“The Trump administration is fully committed to protecting US defense and intelligence assets and complying with US law, including CAATSA,” the letter read

The message, signed by Paul Guaglianone of the Bureau of Legislative Affairs, stated that Washington’s position “has not changed” and that Turkey’s continued possession of the Russian-supplied S-400 remains incompatible with US law and defense requirements. The official stressed that the Trump administration was fully committed to protecting American defense and intelligence assets while maintaining its obligations under the National Defense Authorization Act.

Despite the strained relationship, the letter emphasized that Turkey remains a longstanding NATO ally. US officials framed the relationship as critical to the security interests of both countries and signaled a willingness to maintain dialogue with Ankara.

In 2017, despite several US warnings, Ankara purchased the Russian S-400 surface-to-air missile system, leading to Turkey’s expulsion from the multibillion-dollar fighter jet program in 2019.

“The United States seeks to cooperate with Turkey on common priorities and to engage in dialogue to resolve disagreements,” Guaglianone wrote, while maintaining that Washington has “expressed our disapproval of Ankara’s acquisition of the S-400 and clearly conveyed steps that would need to be taken” in the sanctions review process.

The letter came after a bipartisan coalition of more than 40 US lawmakers pressed Secretary of State Marco Rubio earlier this month to prevent Turkey from rejoining the F-35 program, citing ongoing national security concerns and violations of US law. Members of Congress warned that lifting existing sanctions or readmitting Turkey to the US F-35 fifth-generation fighter program would “jeopardize the integrity of F-35 systems” and risk exposing sensitive US military technology to Russia.

Turkish President Recep Tayyip Erdogan claimed during a NATO summit in June that Ankara and Washington had begun discussing Turkey’s readmission into the program.

Under Section 1245 of the 2020 National Defense Authorization Act, the Pentagon is prohibited from transferring F-35 jets or related technology to Turkey unless Ankara no longer possesses the Russian-made S-400 system and provides assurances it will not acquire such equipment in the future. Because Turkey continues to retain the S-400, US officials are legally barred from approving its participation in the F-35 program.