Ukrainian officials say Russia used drones to target ports in the Odesa region on Wednesday, hitting warehouses and destroying nearly 40,000 tons of grain.
The officials say the grain was intended for export to Africa, Israel, and China.
Two weeks ago, Russia suspended a deal to allow ships to pass through the Black Sea. It has since stepped up attacks on infrastructure that supports such exports.
Russian President Vladimir Putin claims Western leaders have not done their part to allow shipments of Russian food and fertilizer.
He held a call with Turkish leader Recep Tayyip Erdogan, who helped broker the deal.
Erdogan said a long-term suspension would benefit no one, and people in developing countries would suffer the most harm.
Putin said Russia would return to the agreement when the West "meets its obligations."
Ukrainian officials say the Russians also launched drone strikes overnight on the capital, Kyiv. However, they say their anti-aircraft units shot the aircraft down, and no one was killed.
Russia has accused Ukraine of similar attacks on its capital. They say a building in Moscow that houses several government ministries has been targeted twice this week.
Ukraine has not claimed responsibility for the attacks. However, US analysts say it is likely the drones were manufactured in Ukraine.