US President Donald Trump and Turkish President Tayyip Erdogan in a phone call on Monday discussed a Turkish proposal to strike a joint working group on its planned purchase of a Russian S-400 missile defense system, the Turkish Presidency said.
"Our Honorable President brought up the proposal to establish a working group regarding the procurement of the S-400 defense system from the Russian Federation," it said.
Washington has said the missile system could compromise its F-35 fighter jets. Ankara has said a working group could assess the impact of the S-400 on the fighter jets, but on Friday said that it has not heard back from the Americans.