The four-way meeting with Turkish officials comes with food prices around the world soaring because of Russia's invasion of Ukraine.

Ukraine is one of the world's biggest exporters of wheat and other grain.

But its exports have blocked by Russian warships and mines that Kyiv has laid across the Black Sea.

NATO member Turkey has been spearheading efforts to resume the grain deliveries.

Turkish officials say they have 20 merchant ships waiting in the Black Sea that could be loaded quickly with Ukrainian grain.

Turkish Defence Minister Hulusi Akar on Tuesday announced the meeting in a statement that did not specify who will represent each side.

"Military delegations from the Turkish, Russian and Ukrainian defence ministries, and a delegation of the United Nations, will hold talks tomorrow in Istanbul on the safe shipment to international markets of grain waiting in Ukrainian ports," Akar said.