The Black Sea Fleet "carried out live firing of anti-ship cruise missiles at the target ship in the combat training range in the northwestern part of the Black Sea", Russia's defence ministry said in a statement on Telegram.

"The target ship was destroyed as a result of a missile strike," it said.

"Also during the joint exercise, the ships and fleet aviation worked out actions to isolate the area temporarily closed to navigation, and also carried out a set of measures to detain the offending ship."

Russia said Wednesday that cargo ships en route to Ukrainian ports on the Black Sea would be regarded as possibly carrying military cargo, days after scrapping a grain exports deal with Ukraine.

The Kremlin has also declared unspecified areas in the "northwestern and southeastern parts of the international waters of the Black Sea" as "temporarily dangerous for passage".

It has also warned of "risks" to establishing Black Sea shipment routes without Moscow's participation.

Kyiv said it was prepared to continue grain exports through its southern ports, despite Russia pulling out of the deal.