https://www.theregister.co.uk/2018/04/23/sanctions_of_usa_affect_on_supply_turkey_f35_euro_engine_supply/

+Comment Uncle Sam has raised the possibility of sanctions against Turkey for buying Russian anti-aircraft missile systems – putting the UK's supply of overhauled F-35 fighter jet engines at risk.

US government official Aaron Wess Mitchell threatened action if the Middle Eastern/ European nation completed its purchase of Russian S-400 anti-aircraft defence systems, according to Flight Global, which reported the assistant secretary of state for European and Eurasian affairs as saying during a US Congress session: