US Turkish defense ministers discuss Turkey-US cooperation, security

Akar discussed the matters in a phone call with Shanahan, the acting US defense secretary, the Turkish Defense Ministry said in a statement.

The statement did not elaborate on the content of the conversation.

Ankara's ties with Washington have been strained over Turkey's decision to buy the Russian-made defense system, and U.S. officials threatened Turkey's removal from the F-35 program, halting the delivery of jets to the country and excluding Turkish manufacturers from joint production. However, Turkey received two more jets two weeks ago after the delivery of the first batch in June 2018, and four Turkish pilots currently continue their training at the Arizona base.

Ankara has proposed a working group with the United States to assess the impact of the S-400s, but says it has not received a response from US officials.

The Ankara-Moscow S-400 deal was inked in December 2017, when the parties signed a $2.5 billion agreement for two batteries of the systems – Russia's most advanced long-range anti-aircraft missile system in use since 2007.