WASHINGTON (BLOOMBERG) - The Pentagon is delaying delivery of two F-35 fighter jets intended to help train Turkish pilots at an Arizona base because of Turkey's plan to buy a Russian missile defence system, according to US defence officials.
The advanced fighters, built by Lockheed Martin, were to join two F-35s previously delivered to Luke Air Force Base for pilot training before the planes were supposed to be sent to Turkey.
The US has vigorously protested Turkey's plan to buy the S-400 defence system from Moscow, with Acting Defence Secretary Pat Shanahan calling it incompatible with the sale to Turkey of the F-35.
The United States has sought to persuade Turkish President Recep Tayyip Erdogan to buy the US Patriot defence system instead.
The US "has been clear that Turkey's acquisition of the S-400 is unacceptable", Mr Charles Summers Jr, a Pentagon spokesman, said in a statement late Monday (April 1) afternoon.
The Russian S-400 was designed to shoot down US and allied aircraft at greater ranges and altitudes than older systems.
US officials have said they are concerned that sensitive F-35 technology designed to evade such a system could be compromised and used to improve the Russian air defence system if Turkey takes possession of both systems.
Turkey, a member of Nato, is a crucial participant in the US-led programme to build the F-35, the US' costliest weapons system. Ten Turkish companies have been set to produce about US$12 billion (S$16 billion) in parts for the fighter jet, including key components such as the centre fuselage and some landing gear.
Turkey has planned to buy about 100 F-35s, joining Japan, the United Kingdom and Australia as the top international customers for the plane from Lockheed.
"We very much regret the current situation facing our F-35 partnership with Turkey, and the (Department of Defence) is taking prudent steps to protect the shared investments made in our critical technology," Mr Summers said in the statement.
"Our important dialogue on this matter will continue. However, until they forgo delivery of the S-400, the United States has suspended deliveries and activities associated with the stand-up of Turkey's F-35 operational capability."
He added: "Should Turkey procure the S-400, their continued participation in the F-35 program is at risk."
Turkey's move to buy the S-400 reflects a broader political shift as President Erdogan finds himself increasingly at odds with the US and intent as well on cultivating relations with Russian President Vladimir Putin.
Senator Jeanne Shaheen, a member of the Armed Services Committee, praised the Pentagon's decision but said it does not go far enough.
"Though Turkey is an important US ally, their close relationship with Putin and persistent efforts to acquire the Russian S-400 air defence system could seriously compromise our national security," Mr Shaheen said in a statement.