Chicago wheat prices jumped more than 3% while European wheat reached a one-year high on Wednesday, amid escalating shipping attacks in the Sea of Azov, a major export route for Russian wheat.
The most-active wheat contract on the Chicago Board of Trade was up 3.3% at $6.6 a bushel by 1003 GMT.
Euronext wheat futures jumped in morning trade to more than one-year highs, with benchmark September trading 5.6% higher at €228.5 ($260.86) per ton.
"There is growing market concern that Ukrainian drone attacks on Russian shipping in the Azov Sea are increasing, which could cut Russian wheat exports and transfer demand to the EU," a German trader said. "The Ukrainian attacks show no sign of letting up."
Russia accused Ukraine of terrorism over its increasing attacks on shipping in the Sea of Azov, the route for a quarter of Russia's grain exports.
"Fear is also that Russia will retaliate with attacks on Ukrainian grain export ports, which have hardly been touched throughout the war but were hit on Wednesday."
Industry sources, who spoke on condition of anonymity because of the sensitivity of the matter, told Reuters that several grain ships were hit in the Sea of Azov on July 13 and July 14 and caught fire.
Russia is the world's largest wheat exporter.