"Despite the war the harvest conditions don’t look that dire. That could really mean there's not enough storage capacity in Ukraine, particularly if there's no wheat corridor opening up for export from Ukraine," he said.

Another concern is reports that some grain storage had been destroyed in the fighting in Ukraine, he added, without giving details.

Since Moscow launched what it calls a "special military operation" in late February, Ukraine has been forced to export grain by train over its western border or from its small Danube river ports rather than by sea.

Earlier this week, the head of the World Trade Organization told Reuters she was "seriously worried" about spiraling food prices and seeking solutions alongside other partners.

"It would really help the world if we could evacuate this grain (from Ukraine)," Ngozi Okonjo-Iweala said. "There's a serious risk of food prices going up and spiraling out of affordability that could lead to more hunger."