Tensions are rising over the Black Sea after Russia exited a deal protecting maritime exports from Ukraine.

"Starting from 00:00 on July 21, 2023 (2100 GMT), all vessels in the Black Sea heading towards Russia's seaports and Ukrainian seaports located in the temporarily occupied territories of Ukraine may be considered by Ukraine as carrying military cargo, with all the associated risks," the defence ministry said.

Ukraine also said it had prohibited navigation on "the northeastern part of the Black Sea and the Kerch Strait" near Crimea.

The moves make navigation in most of the Black Sea perilous for vessels, after Russia on Wednesday banned traffic on the northwestern and southeastern parts of the sea.

After Ukraine signalled it was ready to continue exports, Moscow said Wednesday it would consider cargo ships travelling to Ukraine through the Black Sea potential military targets.