Washington says it will no longer train Turkish pilots on F-35 fighter jet following Ankara's decision to purchase Russian S-400 missile defence system.
The United States on Friday raised the stakes in its standoff with Turkey over Ankara's deal to acquire a Russian air defence system, laying out a plan to remove the NATO ally from the F-35 fighter jet programme that includes halting any new training for Turkish pilots on the advanced aircraft.
Acting US Defense Secretary Patrick Shanahan sent a letter to his Turkish counterpart on Friday, that laid out the steps to "unwind" Turkey from the programme.
The US move came after Russia announced it will deliver S-400 systems to Turkey in two months.
Turkey's National Defense Minister Hulusi Akar acknowledged the letter by issuing a statement which read: "A letter was sent by US Acting Secretary of Defense Patrick Shanahan to Turkish National Defense Minister Hulusi Akar. Covering defense and security issues between the two countries, the letter expresses the expectation of finding a solution to the existing problems within the framework of strategic partnership and maintaining the comprehensive security cooperation and emphasises the importance of continuing negotiations."
The United States says Turkey's acquisition of Russia's S-400 missile system poses a threat to the Lockheed Martin Corp F-35 stealthy fighters, which Turkey also plans to buy.
The United States says Turkey cannot have both.
But Turkey says it decided to purchase the S-400 system in 2017 following protracted efforts to purchase air defence systems from the US with no success.
US wants Turkey to buy the Patriot missile system rather than the S-400 system from Moscow, arguing it is incompatible with NATO systems.
Turkey has responded that it was the US refusal to sell it Patriots that led it to seek other sellers, adding Russia offered it a better deal, including technology transfers.
TRT World's Jon Brain brings more Washington, DC.
'No new F-35 training'
Shanahan's letter explicitly stated there will be "no new F-35 training." It said there were 34 students scheduled for F-35 training later this year.
"This training will not occur because we are suspending Turkey from the F-35 programme; there are no longer requirements to gain proficiencies on the systems," according to an attachment to the letter that is titled, "Unwinding Turkey's Participation in the F-35 Programme."
In his letter, Shanahan warned that training for Turkish personnel on the F-35 at Luke Air Force Base and Eglin Air Force Base will be discontinued at the end of July.
"This timeline will enable many, but not all, Turkish F-35 students currently training to complete their courses prior to departing the United States by July 31, 2019," Shanahan said in his letter, which noted: "You still have the option to change course on the S-400."
Turkey has expressed an interest in buying 100 of the fighters, which would have a total value of $9 billion at current prices.
If Turkey were removed from the F-35 programme, it would be one of the most significant ruptures in recent history in the relationship between the two allies, experts said.
Defence Minister Hulusi Akar said on May 22 that Turkish military personnel were receiving training in Russia to use the S-400, and that Russian personnel may visit Turkey.
Also on Friday, the head of Russian state conglomerate Rostec, Sergei Chemezov, said the country would start delivering S-400 missile systems to Turkey in two months, the Interfax news agency reported.
Turkey's President Recep Tayyip Erdogan has made it clear that it was "out of the question" for Turkey to back away from its deal with Moscow.
Erdogan said on Tuesday the United States had not "given us an offer as good as the S-400s."
The S-400 is Russia's most advanced long-range anti-aircraft missile system and can carry three types of missiles capable of destroying targets, including ballistic and cruise missiles.
It can track and engage up to 300 targets at the same time and has an altitude ceiling of 27 kilometres (17 miles).