Congress in its final version of the fiscal 2019 defense bill is looking to pause sales of F-35 joint strike fighters to Turkey until a new assessment on U.S.–Turkey relations, going against the wishes of Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE.

The Pentagon would be required to submit a report to lawmakers on the “overall strategic relationship with Turkey,” all foreign weapons sales to Ankara and Turkey’s intended purchase of the Russian-made S-400 long-range air-defense system, House Armed Services Committee senior aides told reporters Monday.

The report would be due within 90 days of the passing of the National Defense Authorization Act (NDAA), during which the Lockheed Martin-made jets would be held from the nation.

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Mattis earlier this month asked lawmakers not to block the F-35 sale, warning that it could start a “supply chain disruption” that could push the price of the aircraft higher.

“At this time, I oppose removal of Turkey from the F-35 program,” Mattis wrote in a July 7 letter.

“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 parts and recover.”

Turkey plans to eventually buy at least 100 F-35 Lightning II fighters under the U.S.-led, multinational Joint Strike Fighter program.

But the Senate, fed up with Turkish aggression, included in its version of the NDAA two provisions targeting Turkey’s plans to purchase the F-35. Another provision would have sanctioned Ankara if it went through with the S-400 purchase.

The House version, meanwhile, would have stopped all weapons sales to the nation until the Pentagon analyzes worsening tensions between the two nations.

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The aides said they kept a broad version of the Senate language.

A separate but related provision in the final NDAA calls on Turkey “to release wrongfully detained U.S. citizens including Andrew Brunson and Serkan Golge,” according to a summary of the bill, the product of negotiations between House and Senate members on their chamber's respective defense authorization legislation.

Brunson, an American pastor, has been detained by the Turkish government for 18 months over accusations that he aided the Kurdistan Workers’ Party in a failed coup attempt against President Recep Tayyip Erdoğan.

Relations between Washington and Ankara have been tense in the past year.

Turkey in December announced it intended to buy the S-400, a sale that worries NATO members because the system is not interoperable with its defense systems. The S-400 could provide a way to steal F-35 technology should the aircraft be synced with it.

The two governments have also butted heads over Kurdish forces in Syria.

The United States relies on the Kurdish forces in fighting the Islamic State in Iraq and Syria (ISIS) and has aided them. But Turkey, which considers them terrorists, seized Afrin, Syria, from Kurdish forces in an offensive that caused a pause in the war against ISIS.

Tensions also flared last year when 15 Turkish security officials were indicted for an attack on protestors outside the Turkish Embassy while Erdogan was in D.C. for a visit with President Trump.

The House is expected to vote on the final NDAA this week, with the Senate to take it up in August.

--This report was updated on July 24 at 10:15 a.m.