Defense Minister Hulusi Akar and U.S. Defense Secretary Lloyd Austin discussed bilateral relations and regional developments, including the grain corridor deal, the counterterrorism fight, problems with Greece and the issue of F-16 jets in a phone call on Monday, the Defense Ministry said.

"Minister Akar and Secretary Austin discussed defense and security issues, including the grain transportation from Ukraine, counterterrorism fight, Turkey-Greece relations and the procurement of F-16s in a phone call," the ministry said.

Turkey, the United Nations, Russia and Ukraine signed a groundbreaking grain corridor deal in Istanbul on Friday.

Russia and Ukraine account for nearly a third of global wheat supplies, while Russia also exports fertilizer and Ukraine corn and sunflower oil. But Ukrainian grain shipments from its Black Sea ports have stalled since Russia invaded, with some 20 million tons of grain stuck.

Turkey made a request to buy 40 Lockheed Martin-made F-16 fighters and nearly 80 modernization kits for its existing warplanes, in what is estimated to be a $6 billion deal. The sale of U.S. weapons to NATO ally Turkey became contentious after Ankara acquired Russian-made S-400 defense missile systems, triggering U.S. sanctions as well as Turkey’s removal from the F-35 fighter jet program.