ANKARA, May 29 (Xinhua) -- Turkish President Recep Tayyip Erdogan and his U.S. counterpart Donald Trump held a phone conversation on Wednesday, and agreed to meet on the sidelines of the G20 summit in Japan in June, Turkish Presidency's Communications Director Fahrettin Altun said.

During the phone call, Erdogan reiterated Turkey's offer to set up a joint working group to address U.S. concerns about Ankara's purchase of Russian S-400 missile defense systems, Altun said on his Twitter.

Erdogan also welcomed the U.S. decision to lift additional tariffs on Turkish steel, noting that it will help reach the goal of 75 billion U.S. dollars in bilateral trade.

The conversation came amid tensions between the two NATO allies over Turkey's planned purchase of the advanced Russian missile system.

Washington threatens to suspend the delivery of the F-35 fighter jets to Ankara and slap additional sanctions if Turkey continues ahead with the purchase of the S-400s.

Turkey has insisted that it is not going to give up its 2.5-billion-dollar contract with Russia. The first batch of S-400s is expected to be delivered to Turkey in July.