In a phone call with U.S. President Donald Trump, Turkish leader Recep Tayyip Erdogan reiterated Ankara’s proposal to form a working group on Russian S-400 missile defense systems, a Turkish official said on Wednesday.

Axar.az reports citing Anadolu Agency.

Fahrettin Altun, presidential communications director, said on Twitter that Erdogan and Trump also discussed bilateral and regional issues.

Washington has balked at Turkey's purchase of the S-400s.

U.S. officials have suggested Turkey buy the U.S. Patriot missile system rather than the S-400, arguing it is incompatible with NATO systems.

Turkey has responded that it was the U.S. refusal to sell it Patriots that led it to seek other sellers, adding that Russia offered it a better deal, including technology transfers.

Separately addressing the U.S. move to lower the tariffs on Turkish steel, Erdogan told Trump that his decision will contribute to realizing the $75B bilateral trade volume target.

Two weeks earlier, Trump reduced tariffs on Turkish steel imports from 50% to 25%.

Also, the presidents agreed to meet at G20 summit scheduled to be held in Japan in June, Altun added.