(CNN) Secretary of Defense James Mattis criticized Turkey for its "authoritarian drift" and its record on human rights but still wants the NATO ally to receive the F-35 Joint Strike Fighter, according to a letter to a senior lawmaker on Capitol Hill.
"I understand and agree with Congressional concerns about the authoritarian drift in Turkey and its impact on human rights and rule of law including the detainment of American citizens such as Pastor Brunson," Mattis said in a letter to the chairman of the House Armed Services Committee, Republican Rep. Mac Thornberry of Texas, dated earlier this month and obtained by CNN.
"The Administration is pressing Turkey on these issues as well as the potential acquisition of the S-400 air defense system," Mattis added, referring to the Russian-made weapons system that has sparked concerns on Capitol Hill and in the Pentagon due to fears that its use by Turkey could enable Moscow to gather sensitive intelligence on NATO and the US military.
"The F-35 is the most advanced aircraft, the most advanced NATO aircraft, and if Turkey goes forward with the acquisition of the S-400, it will allow the Russians to collect information on how to best attack an F-35 fighter," Sen. Chris Van Hollen, a Maryland Democrat who has led efforts to block Ankara from receiving the jet, told CNN last month.
Yet despite these criticisms of Turkey, Mattis said he opposed recent congressional efforts to insert language into the defense budget, the National Defense Authorization Act, aimed at blocking Turkey from receiving the F-35 stealth jet.
"At this time, I oppose removal of Turkey from the F-35 program," Mattis wrote, adding that "removing Turkey could trigger a supply chain disruption for the US military and our partners, as well as increase other program costs."
Mattis noted that Turkey has been a member of the jet's development program since 2002, investing $1.25 billion in the project.
"If the Turkish supply chain was disrupted today, it would result in an aircraft production break, delaying delivery of 50-75 F-35s, and would take approximately 18-24 months to re-source and recover," he said.
Turkey technically took ownership of its first F-35s last month, but the US has retained custody of the jets while Turkish pilots and maintainers are being trained on the new planes at Luke Air Force Base in Arizona.
A US defense official told CNN that this training program could take one to two years to complete, meaning congressional efforts to block the transfer could still succeed during this period.
Turkey plans to eventually acquire 100 F-35s.
Twelve countries participate in the F-35 program. The nine partner nations that participated in the plane's development are the US, Turkey, the UK, Italy, the Netherlands, Canada, Australia, Denmark and Norway. Israel, Japan and South Korea have received the jets through foreign military sales.