A Russian drone strike has hit Ukrainian port facilities at Izmail on the River Danube, a short distance from Nato member state Romania.
A grain warehouse and an elevator for loading grain were damaged.
Almost 40,000 tonnes of grain destined to African countries, China and Israel were damaged, Ukraine said.
Russia began targeting Ukraine's ports after abandoning a UN deal that enabled the safe grain export between both countries across the Black Sea.
"These are the very ports that have become the foundation of global food security today," Ukrainian minister Oleksandr Kubrakov said on his Twitter.
Video, filmed from the Romanian side of the Danube roughly 3km (1.9 miles) away, showed an extensive fire raging in the port area of Izmail early on Wednesday.
Romanian President Klaus Iohannis condemned Russia's continued attacks on Ukrainian infrastructure "in the proximity of Romania" as unacceptable.