Turkey's presidential adviser says Ukraine and Russia will sign an agreement on Friday. The deal may allow Ukraine to export grain across the Black Sea.

Ibrahim Kalin made the announcement on his Twitter account on Thursday, calling the expected deal "critically important for global food security."

Kalin wrote that the signing will take place in Istanbul under the auspices of Turkish President Recep Tayyip Erdogan and UN Secretary-General Antonio Guterres.

Ukraine is one of the world's top grain exporters. It has been unable to export huge stocks of harvested crops across the Black Sea due largely to Russian blockades. This has exacerbated global food insecurity.

Turkish Foreign Minister Mevlut Cavusoglu spoke in an interview with the state-run broadcaster on Thursday, ahead of Kalin's Twitter announcement.

Cavusoglu said Turkey has continued to hold talks with the concerned parties and hopes to announce good news in the coming days.

He said an agreement between Russia and Ukraine on grain exports could raise hopes for ceasefire negotiations.