Three more ships filled with grain will sail from Ukraine on Friday under a UN-backed deal lifting Russia's blockade of the Black Sea, Turkey's defence minister said.
"It is planned that three ships will set sail tomorrow from Ukraine," Anadolu state news agency quoted Defence Minister Hulusi Akar as saying, one day after the first ship passed Istanbul on its way to Lebanon.
Ankara also announced that Turkish Foreign Minister Mevlut Cavusoglu discussed the agreement's implementation by phone with UN chief Antonio Guterres, without disclosing further details.
Moscow and Kyiv agreed in Istanbul last month to resume shipments of wheat and other grain from Ukrainian ports for the first time since Russia invaded its neighbour in February.
The first ship, loaded with 26,000 tonnes of maize, set off from Odessa on Monday for the Lebanese port of Tripoli.
The Sierra Leone-flagged Razoni was cleared for passage through the Bosphorus Strait by a team that included Russian and Ukrainian inspectors on Wednesday.
The ship's passage is being overseen by an international team that includes officials from Turkey, the United Nations and the two warring parties.
The team said in a statement the first ship's successful passage offered "proof of concept" that the agreement can hold.
Two of the ships leaving on Friday will depart from southern Chornomorsk, with the third leaving from Odessa.
They will carry a total of more than 58,000 tonnes of wheat, said the joint coordination centre, which is overseeing the export of Ukrainian cereal.
They will all head for Karasu in northwestern Turkey, Ringaskiddy in southern Ireland and Teesport in northeastern England, the statement added.
The centre was now testing "an operation with multiple boats" using a secure corridor to circulate in the Black Sea: the three leaving Ukraine and a fourth which should leave Turkey bound for Chornomorsk.
Ukraine said earlier this week it has 16 more ships loaded with grain and ready to set sail.
But it also accuses Russia of stealing Ukrainian grain in territories seized by Kremlin forces, then shipping it to allied countries such as Syria.
Turkish hopes the deal could lead to ceasefire talks have so far been disappointed.
Turkish President Recep Tayyip Erdogan is expected to push for direct ceasefire negotiations when he meets Vladimir Putin at the Russian leader's Black Sea retreat in Sochi on Friday.
"We discussed if the grain agreement can be an occasion for a sustainable ceasefire," Cavusoglu said after meeting Russian counterpart Sergei Lavrov in Cambodia on Wednesday.
Russia and Ukraine are major suppliers of wheat and other grain.
The halt of almost all deliveries from Ukraine has sent global food prices soaring, making imports prohibitively expensive for some of the world's poorest nations.