The Russian government has issued a threat that is putting further pressure on global food prices. It says that, from Thursday, it will consider any ship bound for any Ukrainian port to be a potential carrier of military cargo.

More than 1,000 ships full of grain and other foodstuffs have sailed since the introduction last year of the Black Sea Grain Initiative. Negotiators extended the deal three times, but those from Russia refused this week to extend it again. They say Western leaders failed to fulfill certain conditions, including easing sanctions on agricultural exports.

On Wednesday, Russian President Vladimir Putin said, "It was outright arrogance and insolence; just promises and empty chatter."

Putin added that he will consider resuming the agreement if the demands are met.

Ukraine says that Russian forces are trying to eliminate the possibility of shipping any of their grain.

President Volodymyr Zelenskyy said on Wednesday that the troops are deliberately targeting grain terminals, warehouses and other infrastructure in the port of Odesa used to export food.

Zelenskyy said, "Such attacks by Russian terrorists target not only our country, but also global stability."

Russia's threats have constricted international supplies and upset markets. On Wednesday, Chicago wheat futures rose as much as 9 percent -- the biggest jump since the grain deal was implemented.