Major General Reha Ufuk Er makes a speech as Turkey takes delivery of its first F-35 fighter jet with a ceremony in Texas. Photo: Anadolu Agency via AFP

After it appeared all but certain that Washington would follow through on a commitment to transfer the US-made F-35 to NATO ally Turkey, the deal is yet again in limbo.

Despite the fact that late last month Turkey already received its first F-35 – which is being kept inside US borders for training – lawmakers in both the Senate and House of Representatives just agreed to block the transfer of the advanced fighter to Turkey.

The move comes after Ankara said last month that US President Donald Trump had personally pledged to take necessary steps to ensure delivery of the aircraft.

The deal reached between lawmakers on Monday reconciles the House and Senate versions of the National Defense Authorization Act, an annual bill detailing the military’s budget and expenditures. A new reconciled version still requires a vote in both the House and Senate.

Members of Congress who have raised the issue cited Turkey’s agreement to purchase Russia’s S-400 missile system as a reason to renege on a commitment to transfer the stealth fighters.

According to a report in Breaking Defense, lawmakers formed a consensus that all countries must demonstrate a willingness to break military relationships with Moscow before being granted a waiver. The language appeared to be directed not just at Turkey but also at India, which buys a considerable amount of Russian-made arms.

The legislation is likely to ruffle feathers at the Pentagon, where officials have been trying to salvage the deteriorating relationship with Turkey, an important strategic ally of the US. Last month, Secretary of Defense Jim Mattis urged against holding up the transfer of F-35s to Turkey in a letter to Congress.