Russian President Vladimir Putin thanked his Turkish counterpart Recep Tayyip Erdoğan for his efforts to mediate discussions on the export of grain from Ukraine. "With your mediation, we have moved forward," Putin told Erdoğan in Tehran on Tuesday, according to the Kremlin.

"All issues about Ukrainian grain exports out of Black Sea ports have not yet been resolved, but having progress is already a good sign," Putin said.

Last Thursday, Ankara said there is a consensus regarding establishing an operations center in Istanbul that will monitor the implementation of a potential sea corridor in the Black Sea to export grain from Ukraine.

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.

The United Nations has appealed to both countries, as well as maritime neighbor Turkey, to create a sea corridor for Ukrainian grains to be exported from the Black Sea. Turkey has been coordinating with Russia and Ukraine to agree to a plan that would restart grain exports from Ukrainian ports.

Ankara has held talks with Moscow and the U.N., but says all sides need to meet for a final agreement.