WASHINGTON - The United States said it is winding down Turkey's involvement in its F-35 stealth fighter jet programme over Ankara's plans to buy a Russian air defence system that could pose a danger to the aircraft.
US officials announced on Monday that Washington had halted the training of Turkish pilots on F-35 fighters at an airbase in the US state of Arizona.
The move at Luke Air Force Base comes faster than expected, days after acting US defence chief Patrick Shanahan told his Turkish counterpart their pilots already in the country could remain until the end of July.
Washington gave Ankara a July deadline to make its decision over buying the Russian S-400 missile system. The US says Turkey's missile defence acquisition from Russia poses a threat to Lockheed Martin's F-35 stealth fighters, which Ankara also wants to buy.
Washington says Turkey cannot have both.
The standoff threatens to bring US sanctions, which would hurt Turkey's already recession-hit economy, and raise questions over its role in the North Atlantic Treaty Organization.
"The department is aware that the Turkish pilots at Luke AFB are not flying," Air Force Lieutenant-Colonel Mike Andrews, a Pentagon spokesman, told Reuters news agency.
"Without a change in Turkish policy, we will continue to work closely with our Turkish ally on winding down their participation in the F-35 programme."
A second US official, speaking on condition of anonymity, said a local commander at Luke decided last week to halt the training of Turkish pilots and maintenance crews over safety concerns.
Some training of Turkish maintenance personnel continues at Eglin Air Force Base in Florida, the official said.
Turkey is a partner in the F-35 programme that helped fund the development of the fighter jet. It plans to buy 100 aircraft and already owns four, which are currently on American soil and used for training purposes.(FA)