Wheat and corn jumped after Ukraine said a Russian drone attack damaged a port facility in the Odesa region, adding to a spate of attacks aimed at crippling exports from the Black Sea and Danube river.

Russian forces struck the southern part of the Odesa region overnight with drones, regional governor Oleh Kiper said in a Telegram statement. Some objects of port and industrial infrastructure caught fire, and a silo was damaged, according to the statement.

Romanian media reported that the attack was at Izmail, one of Ukraine’s biggest river ports for grain and located on the Danube at the border with Romania. Ukraine’s Infrastructure Ministry and Romania’s Defense Ministry declined to comment.

Wheat futures in Chicago jumped as much as 4.9% to $6.84 a bushel. Corn rose as much as 3.2%.

Russia has previously attacked ports in the Odesa region and on the Danube river in a bid to disrupt Ukraine’s exports. Last week it attacked the Danube port of Reni, sending wheat up by the exchange limit that day.

Ukraine has continued to explore alternative grain export routes after Moscow pulled out of an agreement allowing shipments through the Black Sea on July 17. Romania plans to expand one of the key transit routes for grain from Ukraine, while Kyiv has also discussed using Croatian ports for shipments.