UN Secretary General António Guterres and Turkish President Recep Tayyip Erdoğan are expected to meet Ukrainian President Volodymyr Zelensky in Ukraine on Thursday.
Guterres arrived in Lviv on Wednesday evening, the UN said.
Türkiye's Communications Directorate said in a statement that the leaders would also discuss potential steps to end the Russia-Ukraine war through diplomatic means during the meeting.
Erdoğan is set to have a one-hour meeting with Zelenskyy in the early afternoon before both are joined by Guterres.
On July 22, Türkiye, the UN, Russia, and Ukraine signed a deal in Istanbul to reopen three Ukrainian Black Sea ports for exporting Ukrainian grain stuck due to the Russia-Ukraine war, which is now in its sixth month.
The three leaders will also discuss maintaining Ukrainian grain exports to world markets, Ankara said.
Guterres and Erdoğan helped bring Russia and Ukraine to an agreement on the export of Ukrainian grain at the end of July, breaking a blockade on Ukrainian ports since Russia's invasion in February.
The UN chief is also scheduled to visit the joint coordination centre for monitoring grain exports across the Black Sea in Istanbul on Saturday.
