Ukrainian President Volodymyr Zelensky was due in Istanbul on Friday for talks with his Turkish counterpart Recep Tayyip Erdogan over the war with Russia and navigation on the Black Sea.

The two leaders were set to meet at the Dolmabahce Palace in Istanbul and hold a press conference on Friday evening, according to plans published by the Turkish presidency.

Zelensky's office said the pair will discuss Kyiv's proposal to end the conflict -- as well as "Black Sea navigation security, global food stability, and the release of Ukrainian prisoners and political prisoners held by the Russian state."

NATO member Turkey has sought to maintain good relations with both Moscow and Kyiv throughout the two-year war, with Erdogan pitching himself as a key go-between and possible peace-maker.

A Turkish diplomatic source told AFP on Friday that Ankara "will once again emphasise that our strong support for the territorial integrity, sovereignty and independence of Ukraine, including Crimea, continues."

- 'Time for dialogue' -

Turkey also hosted failed ceasefire talks between Kyiv and Moscow in the first weeks of the war.

It hopes to revive those talks at some point in the future.

"Both sides have now reached the limit of what they can achieve through war," Turkish Foreign Minister Hakan Fidan said earlier in March.

"We think it's time to start a dialogue towards a ceasefire."

Turkey's strategic location on the Black Sea and its control of the Bosphorus Strait gives it a unique military, political and economic role in the conflict.

In July 2022, Ankara brokered the Black Sea Grain deal, the most significant diplomatic agreement so far reached between Kyiv and Moscow.

Moscow ditched the initiative -- which allowed the safe passage of Ukrainian agricultural exports across the mine-laden Black Sea -- a year later, complaining the terms were unfair.

Kyiv since launched an alternative export route for ships which hugs the coastline, avoiding the contested international waters.

Turkey has been lobbying hard for an agreement to ensure cargo can once again navigate those waters in safety.

After a visit to Turkey last year, Zelensky returned to Kyiv with five top commanders from the Azov regiment who were supposed to have remained in Turkey until the end of the conflict under a prisoner exchange deal with Moscow.

The Ukrainian leader will also visit shipyards where corvettes for his navy are being built and meet Turkish defence companies on Friday, Zelensky's office said.

- Russian ties -

Turkey's Western allies have expressed concern over the closeness of its relations with Moscow.

Ankara is reliant on Russian energy and has faced scrutiny for its role in helping Russia skirt Western trading restrictions.

The United States has sanctioned several Turkish companies for helping Moscow purchase goods that could be used by its armed forces.

The meeting between Zelensky and Erdogan comes a week after Russian Foreign Minister Sergei Lavrov met his Turkish counterpart Fidan at a diplomatic forum in Antalya.

President Vladimir Putin was due to visit Turkey last month, but the trip was postponed by Moscow, according to reports in Turkish and Russian media citing diplomatic sources.

The Kremlin has said it is working on rescheduling the visit, but has given no date.