Pentagon preparing to move F-35 manufacturing work out of Turkey

US Acting Defense Secretary Patrick Shanahan warned Friday that the Pentagon will halt manufacturing support for the F-35 in Turkey if Ankara buys a Russian missile defence system.

Shanahan told journalists the government remained steadfast in its opposition to Turkey's adoption of the S-400 anti-aircraft technology.

"If Turkey decides that the S-400 is a decision they want to go forward with, then we have to move work out of Turkey," he said.

Shanahan noted that he had met with delegations from US aerospace manufacturers Lockheed Martin and United Technologies to discuss options if Turkey refuses to forego the S-400.

Washington has warned for months that Turkey's adoption of Russian missile technology alongside US fighter jets would pose a threat to the F-35 and endanger Western defence.