Ukrainian President Volodymyr Zelenskyy in the early hours of Saturday held a joint news conference in Istanbul with Turkish President Recep Tayyip Erdogan, after the two leaders held talks.
Speaking about security in the Black Sea region, Zelenskyy said more significant efforts were needed to limit Russia's aggression.
The Ukrainian president said the Black Sea "should be a space of security, cooperation".
Zelenskyy said Russia has been blocking the movement of ships with food through corridors "as much as possible". "Russia behaves as if it owns the entire Black Sea," he added.
Russia's invasion of Ukraine, one of the world's major grain producers, threatened a global food crisis that was eased by a deal that lets Ukraine export grain through the Black Sea.