Ukraine, Russia, Turkey and UN Secretary-General Antonio Guterres will sign an agreement on Friday to resume Ukrainian wheat exports to the Black Sea, Turkish President Recep Tayyip Erdogan's office said.

Russia and Ukraine are both major global suppliers of wheat, but the invasion of Ukraine has pushed up food prices and fueled an international food crisis.

The war has blocked Kiev's exports, leaving several ships stranded and some 20 million tons of grain stuck in silo towers in the port of Odesa.

Ankara said a general agreement was reached on a UN-led plan during talks in Istanbul last week and would now be put in writing by the parties.

The details of the agreement are not known at this time.

The agreement will be signed on Friday at the Dolmabahçe Palace offices, Erdogan's office said.