Turkish Defense Minister Hulusi Akar and acting U.S. counterpart Mark Esper late Friday night discussed issues related to Turkey's acquisition of long-range missile defense systems and recent developments in war-ravaged Syria following the arrival of Russian S-400 missile defense system components in Turkey.

In a phone conversation, Akar and Esper discussed wide-ranging issues.

"[Turkey's] acquisition of the Russian S-400 defense system was not a preference but necessity. Evaluations on the proposal of Patriot [defense system] are still going on," Akar said.

The Trump administration has threatened to expel Turkey and Turkish firms from the advanced F-35 jet fighter program over concerns the Russian system could be used by Russia to gain sensitive data on the jets.

The U.S. has also threatened sanctions over the S-400 purchase, with Turkey responding that any sanctions would be met in kind.

Local media quoted Esper as saying the U.S. position on the F-35 has not changed.

The Pentagon is expected to brief reporters later Friday on the matter following Esper's conversation with Akar.

Turkey agreed in April 2017 to purchase the S-400 system from Russia following lengthy efforts to purchase an air defense system from the U.S. with no success.

U.S. officials have advised Turkey to buy the Patriot missile system rather than the S-400 system from Moscow, arguing it is incompatible with NATO systems.

Turkey has responded that it was the U.S.' refusal to sell it Patriots that led it to seek other sellers, adding Russia offered it a better deal, including technology transfers.