Wheat prices have risen sharply on global markets after Russia said it would treat ships heading for Ukrainian ports as potential military targets.
Moscow pulled out of a deal this week that had guaranteed safe passage for grain shipments through the Black Sea.
A White House spokesperson accused Russia of planning to blame Ukraine for attacks on civilian ships.
Russia’s President Vladimir Putin said he would return to the grain agreement immediately if his demands were met.
They include reconnecting Russia’s agricultural bank to a global payment system.
A Russian air strike on the Ukrainian port city of Mykolaiv wounded 18 people on Wednesday night, according to a local official.
The region’s governor Vitaliy Kim said nine of the injured, including five children, were taken to hospital for treatment.
Other air strikes were reported on the port of Odesa.
Elsewhere, a drone strike in Russian-controlled Crimea killed a teenage girl, a Russian-backed official said.
Following previous air strikes around Odesa this week, Ukraine’s President Volodymyr Zelensky accused Russia of deliberately targeting grain export infrastructure and putting vulnerable countries at risk.
Kyiv urged other countries in the Black Sea region to intervene to assure the safe passage of cargo ships.
“From 00:00 Moscow time on 20 July 2023 [21:00 GMT Wednesday], all vessels sailing on the Black Sea to Ukrainian ports will be regarded as potential carriers of military cargo,” the Russian defence ministry said.
“Flag states of such vessels will be considered to be involved in the Ukrainian conflict on the side of the Kyiv regime,” it added.
Wheat prices on the European stock exchange soared by 8.2% on Wednesday from the previous day, to €253.75 (£219.78) per tonne, while corn prices were up 5.4%.
US wheat futures jumped 8.5% on Wednesday, their highest daily rise since just after Russia’s invasion of Ukraine.
Ukrainian Agriculture Minister Mykola Solskyi said strikes had destroyed 60,000 tonnes of grain and damaged considerable parts of grain export infrastructure.
Russia began targeting Ukraine’s ports in the early hours of Tuesday within hours of its withdrawal from the grain deal.
