A F-35 fighter jet prepares for landing with its life fan cover deployed over Patuxent River Naval Air Station, Maryland in this undated handout image. (Xinhua/REUTERS)

WASHINGTON, May 28 (Xinhua) -- The United States may suspend training Turkish pilots for F-35 fighter jets as Ankara follows through its S-400 missile deal with Moscow, media reported on Tuesday, citing anonymous sources.

The sources, who are familiar with the matter, revealed the considerations mentioned above, adding the final decision has not been made, according to a Reuters report.

Turkish pilots for F-35 fighters are now training at Luke Air Force Base in the U.S. state of Arizona.

U.S. media CNBC reported last week that Washington had given Ankara just over two weeks to give up its S-400 deal with Russia or risk severe penalties and lose the possibility of buying U.S. F-35 fighter jets.

Turkish Defense Minister Hulusi Akar on Monday dismissed reports that the United States had issued an ultimatum, while he said the delivery of Russian S-400 might not take place in June as he previously said.

Akar, however, said the S-400 would arrive in following months, adding "the process has started."

Washington and Ankara for months have been sparring over the latter's purchase of the Russian-made S-400 air defense system.

The United States argued that Russian missiles on Turkish territory could gain valuable intelligence on the technical systems of the U.S.-made stealth F-35 jets expected to be delivered to Ankara in November.

In early April, the Pentagon announced that it halted "deliveries and activities" related to Turkey's F-35 operational capability until Ankara forgoes the delivery of S-400.