Grain prices jumped Monday, after Russia said over the weekend it would suspend participation in a deal that allowed Ukraine to ship grain via the Black Sea.

Chicago wheat futures advanced 3.5% to $8.59 a bushel and corn rose 1% to $6.87 a bushel, with the jump representing growing uncertainty amongst traders about the future global food supply.

Wheat prices are roughly $1 a bushel higher a year ago, but well below the record $12.94 hit after Russia’s initial invasion of Ukraine. Prices have been steadied in recent months by prospects of the grain deal, which would have guaranteed safety of agricultural products exported from Ukraine.

Russia said Saturday that it would suspend participation in response to an attack on the occupied Black Sea port of Sevastopol that it blamed on the government of Ukraine. The United Nations and Turkey have scrambled to rescue the agreement.

“Global commodity balance sheets are tight and the world needs agriculture products flowing from the Black Sea region, so this announcement matters for grains and the entire agriculture complex,” said Dave Whitcomb, head of research at Peak Trading Research.

For now, grain ships continued to move in and out of Ukrainian waters in the Black Sea, which traders worry may not last.