Ukraine said any ships heading to Russian ports may be military targets, a tit-for-tat response to a threat from Moscow that escalates the war’s risk to global food markets.

Since Moscow halted the Black Sea agreement that allowed Ukraine to export part of its grain harvests, Russia has attacked Ukrainian grain storage facilities and warned that all vessels heading to Ukrainian ports would be considered potential carriers of military supplies.

The escalating threat to vital Black Sea trade steps up the risk of turmoil on global markets for everything from oil and food staples to fertilisers. Russia’s attack on its neighbour has already severely disrupted exports from Ukraine, a major producer of grains and vegetable oils.

Ukraine has previously attacked Russian ships in the Black Sea, sinking the flagship Moskva cruiser with a Neptune anti-ship missile soon after Russia’s invasion.