Acting US Defence Secretary Patrick Shanahan in a letter to his Turkish counterpart Hulusi Akar on Thursday said that all Turkish pilots in the programme must leave the US by July 31 and training for new pilots will be suspended, Anadolu news agency reported on Saturday.
The timetable would allow pilots currently training on the F-35 to complete their trainings and for other pilots to be reassigned to other posts, Shanahan said.
His remarks are the latest in a set of moves by the US to try to remove Turkey from the F-35 programme amid a standoff with its NATO ally over the purchase of Russian S-400 missile defence system.
Tensions between the US and Turkey have reached a fever pitch in recent months with Ankara set to begin receiving the advanced Russian surface-to-air missile system in July.
Washington has already suspended deliveries of parts and services related to Turkey's receipt of the multi-million dollar jets. "You still have the option to change course on the S-400," Shanahan said in the letter.
Following protracted efforts to purchase an air defence system from the US with no success, Ankara decided in 2017 to purchase Russia's system, the news agency said.
US officials advised Turkey to buy the US Patriot missile system rather than the S-400 system from Moscow, arguing it would be incompatible with NATO systems and expose the F-35 to possible Russian subterfuge.
But Turkey has emphasized the S-400 would not be integrated into NATO operability and would not pose a threat to the alliance.
Ankara said that it was Washington's initial refusal to sell the Patriot missile system that led it to seek other offers, adding that Russia offered a better deal that included technology transfers.
Erdogan had earlier said that the US had yet to give Turkey an "offer as good as the S-400s".
( With inputs from IANS )