Turkish presidential spokesman Ibrahim Kalın and U.S. National Security Advisor John Bolton discussed the Russian S-400 air defense system via telephone Tuesday, according to presidential sources.
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.
Like other NATO allies of Washington, Turkey is both a prospective buyer and a partner in production of the F-35, which has been beset by cost overruns and delays, and entered service in the United States in 2015.
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 U.S. 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.
Kalın and Bolton also discussed bilateral relations, a date for U.S. President Donald Trump's visit to Turkey, and recent developments in Libya.
In early April, Khalifa Hifter, who commands forces loyal to Libya's eastern government, launched a campaign to capture Tripoli from Libya's UN-recognized Government of National Accord (GNA).
Libya has remained beset by turmoil since long-serving leader Moammar Gaddafi was ousted and killed in a bloody NATO-backed uprising in 2011.
Since then, the country has seen the emergence of two rival seats of power: one in eastern Libya, to which Hifter is affiliated, and the other, the GNA, in Tripoli.