ISTANBUL (AP) — A senior Turkish official says President Recep Tayyip Erdogan and U.S. President Donald Trump have agreed to meet on the sidelines of the G-20 summit in Japan being held June 28-29.

In a tweet Wednesday, Erdogan's Communications Director Fahrettin Altun also said the president reiterated Turkey's offer for a joint group to overcome an impasse with the U.S. on Turkey's pledge to buy Russian-made S-400 missiles.

U.S. officials say the S-400s would pose a risk to Turkey's F-35 fighter jet program and warned Ankara it risked being kicked out of the F-35 program and could face U.S. sanctions.

Erdogan also welcomed the U.S. decision this month to drop additional tariffs on Turkish steel. Trump had doubled the tariffs to 50% in August amid a diplomatic spat over the imprisonment of an American pastor.