The US has halted delivery of equipment related to the F-35 stealth fighter aircraft to Turkey, sources familiar with the situation told Reuters on April 1.

The move marks the first concrete US step to block delivery of the jet to its Nato ally in light of Ankara’s planned purchase of the Russian S-400 advanced missile defence system. The message from both Washington and Nato to Turkey has come loud and clear for many months now—Turkey cannot simultaneously deploy the S-400 and F-35s because that would potentially expose sensitive performance data of the latter, the world’s most sophisticated fighter aircraft. But Ankara has repeatedly refused to negotiate a cancellation of its order placed with the Kremlin, hence the stepping up of pressure by suspending equipment deliveries.

In recent days, US officials have reportedly told their Turkish counterparts they will not receive further shipments of F-35 related equipment needed to prepare for the arrival of the jet, built by Lockheed Martin Corp in a trillion-dollar programme.

Turkey has said it will take delivery of the S-400s in July.

Complication for Cavusoglu
The US decision on the F-35s will complicate Turkish Foreign Minister Mevlut Cavusoglu’s planned visit to Washington this week for a Nato summit. Cavusoglu and his fellow ministers know that a deterioration of S-400 row with Washington—which is just one part of a multi-faceted dispute between the US and Turkey—could rattle the markets and leave Turkey’s embattled economy exposed to additional turbulence.

In an attempt to persuade Turkey to drop its plans to buy the S-400, the US offered the pricier American-made Patriot anti-missile system to Ankara in a discounted deal. That offer expired at the end of March. Turkey has shown interest in the Patriot system, but not at the expense of abandoning the S-400.

Turkey has engaged with US negotiators in recent days about buying the Patriot system, a person familiar with the matter told Reuters. The system is made by Raytheon Co.

Turkish Defence Minister Hulusi Akar in March said that despite some issues, Turkish pilots were continuing their training at an air base in Arizona on the F-35, each of which costs $90mn, and that Ankara was expecting the aircraft to arrive in Turkey in November.

Bipartisan bill
Four US senators last week introduced a bipartisan bill that would prohibit the transfer of F-35s to Turkey until the US government certifies that Ankara will not take delivery of the S-400 system.

Also last week, it was reported that US officials had come to the conclusion that excluding Turkey from the F-35 programme was feasible.

Turkey makes parts of the F-35 fuselage, landing gear and cockpit displays. It has also been tapped to run a regional repair and maintenance depot that would attend to the F-35s owned by other Nato states including the UK.