Russia’s pre-dawn drone attacks Monday on Ukraine’s key Danube river port region targeted Kyiv’s best remaining export route, after Moscow reinstated its blockade of the country’s Black Sea ports last week. It was a major escalation after Russia launched several rounds of missile attacks last week on Ukraine’s Odesa port, its main Black Sea port. Key commodity markets responded Monday by jumping sharply upward.

Joe Glauber, former chief economist at the U.S. Agriculture Department, predicted that if Monday’s big spikes in global wheat and other commodity prices endure, they would eventually put pressure on U.S. food prices and unleash other strains on global food systems. But Glauber added that it is possible calls for de-escalation could eventually calm markets.

Biden administration officials — and global commodity markets — had held out some hope that allies could help reestablish a semblance of the fragile Black Sea grain deal, which allowed Ukraine to ship out some 33 million metric tons of grain and oilseeds to China, Europe, the Middle East and Africa over the past year. Russia refused to extend the deal on July 17, after Western countries declined some of its demands to lift certain sanctions. Alternatively, Ukraine had pressed Western allies to help escort ships carrying Ukrainian grain through the Black Sea, despite Russian threats to target them.

Glauber said the market’s relatively muted response to Russia’s withdrawal from the Black Sea deal last week was based on the assumption Ukraine would be able to continue exporting grain via the Danube, as well as the possibility that Turkey could provide some safe passage to Ukrainian grain shipments in the short-term.

“I think that’s off now,” Glauber said.

The drone strikes Russia carried out against silos and other key infrastructure at Ukraine’s Danube River ports, Ukraine’s best remaining export route to global markets, comes after Moscow’s continued air strikes has left Ukraine’s strategic Black Sea port at Odesa “heavily damaged,” according to Ukrainian officials in the city. And they show that Russia is willing to target “any key export routes” for Ukraine’s grain supplies regardless of their location, said a U.S. official who was granted anonymity to discuss internal conversations. It’s also still a major question whether shipping companies, if they’re even able to operate from anywhere in Ukraine at this point, will be able to secure the insurance necessary to move large amounts of grain through the region amid increasing military tensions.

Up until last week, commodity markets had been stabilizing, easing, at least somewhat, concerns about food security for billions of people around the world.

But the spikes in wheat and corn prices, along with a new surge in crude oil prices Monday, are all ominous signs. And they come just days before a critical U.S. Federal Reserve meeting that will determine whether the central bank hikes interest rates again.

“This adds to the risk of lingering and sticky inflation longer term,” said Arlan Suderman, chief commodities economist at StoneX. Suderman noted that while inflation is cooling in other key sectors, commodity markets remain a concern.

U.S. and Ukrainian officials have argued that Moscow is using its attacks on Ukraine’s grain exports as a way to crush the country’s agriculture-dependent economy while increasing its own role as a major food exporter to hungry populations across Africa and the Middle East.

After the Russian attacks on Ukraine’s river ports Monday, Russian President Vladimir Putin appeared to suggest that Moscow could fill in the supply hole left by Ukraine.

In an op-ed published Monday, just ahead of a summit Russia is hosting with African leaders this week, Putin wrote that his country “understand[s] the importance of an uninterrupted food supply for the socio-economic development and maintenance of the political stability of African states.” He added: “Based on this, we have always paid great attention to issues related to the supply of wheat, barley, corn and other crops to African countries.”

The Russian strikes on Ukraine’s Danube ports, which Ukrainian officials said were carried out with Iranian-made drones, are stoking other geopolitical concerns in the region, given NATO-member Romania’s location just across the Danube from Ukraine.

The State Department said Secretary of State Antony Blinken spoke with Romania’s foreign minister Monday, and the two discussed issues around global food security and cooperation on Black Sea security.