Ukraine’s military said a commercial ship on the Black Sea was struck Wednesday by a Russian missile, a rare attack that may threaten to undermine the passage of key exports such as grain. 

The vessel was hit at the port of Pivdennyi, according to an official familiar with the matter, who asked not to be identified discussing security issues. The hub is one that has been key to Ukrainian grain shipments. 

“Continuing its terror against civil shipping, the foe has insidiously launched an anti-radar missile Kh-31P toward one of Odesa region’s seaports from its tactical aviation airplanes in the Black Sea,” Ukraine’s military said on its Telegram channel, without naming the facility.

The rocket hit a ship under the Liberian flag that was entering the port, killing one person and injuring four, including three Philippine citizens, the military said.

Kyiv recently opened a unilateral corridor from the region to allow ships to export commodities like grains and metals from its deep-sea ports in Greater Odesa, after Moscow in July pulled out of the United Nations-backed Black Sea grain deal that had guaranteed safe movement of crop vessels.

Wheat futures earlier rose as much as 5% in Chicago, before paring gains. 

The civil vessel was supposed to ship iron ore to China, according to Infrastructure Minister Oleksandr Kubrakov. The incident was the 21st “deliberate Russian attack” on port infrastructure since the end of the grain deal, he said on Facebook.

“That is why Ukraine does everything to strengthen its air defense to shield the south of Ukraine from Russian terrorist attacks,” Kubrakov said.