The US and EU have criticised Russia’s decision to pull the plug on the wartime deal that unblocked the passage of millions of tonnes of grain via southern Ukraine, with traders and food security experts saying Moscow’s move would fuel a fresh spike in prices and increase hunger levels among poorer countries.

Washington called Moscow’s suspension on Saturday of its participation in the UN-backed deal with Kyiv an “outrageous” action that risked fuelling starvation. Moscow linked its decision to an attack earlier that day on ships in the port of Sevastopol in the Crimean peninsula, which Russia annexed from Ukraine in 2014. Ukraine called this a “false pretext”.

“The US regrets Russia’s suspension of its participation in the operations of the UN-brokered Black Sea grain initiative. We urge all parties to keep this essential, life-saving initiative functioning,” US secretary of state Antony Blinken said in a statement.

He said the deal had allowed 9mn tonnes of food products to be exported, bringing down global prices that soared following Russia’s invasion of Ukraine in February.

Josep Borrell, EU foreign affairs chief, called on Russia to reverse its decision to exit the deal, saying it “puts at risks the main export route of much needed grain and fertilisers to address the global food crisis caused by its war against Ukraine”.

The Kremlin’s announcement surprised grain traders and analysts, who while doubtful that the deal would have been extended beyond its mid-November deadline, had not expected a sudden termination.

“We’ll see a substantial spike in prices” as a result, predicted Andrey Sizov, managing director of Black Sea grain consultancy SovEcon, adding Russia’s move was its “worst-case scenario”.

Arif Husain, chief economist at the UN World Food Programme, warned that Moscow’s decision would hit many poor nations. “This in the good times would be bad but in the current state of the world, it’s something that needs to be resolved as soon as possible. It’s not about one country but about dozens of countries,” he said.

Ukraine’s foreign minister Dmytro Kuleba said that “by suspending its participation in the grain deal on a false pretext of explosions 220km away from the grain corridor, Russia blocks 2mn tons of grain on 176 vessels already at sea — enough to feed over 7mn people”.

Moscow on Sunday defended its actions, with the Russian ambassador to the US arguing that the “truly outrageous” move was Washington’s failure to criticise the attack on Sevastopol.

The attack, which appears to have targeted Russian warships, comes eight months into Russia’s full-blown invasion of Ukraine.

The Black Sea deal, thrashed out this summer in Istanbul, had seen Moscow guarantee safe passage for cargo ships carrying grain coming from ports in the south of Ukraine that had previously been blocked by the war.

Specialist outlet Fastmarkets Agricensus on Sunday reported “panic” in these ports as international vessels already docked and loading feared they could get trapped now that Moscow had suspended the safe passage corridor.

Ukraine’s president called for a “strong international response” from the UN and G20.

“Russia is doing everything to ensure that millions of Africans, millions of residents of the Middle East and South Asia find themselves in conditions of artificial famine or at least a severe price crisis,” Volodymyr Zelenskyy said in an nightly video address.

Russia denies its attack on Ukraine, a major global exporter of grain and other food products, caused price rises or exacerbated food shortages. Moscow said on Saturday that it was ready to supply 500,000 tonnes of grain directly to poor countries in the near future, the Tass news agency reported, citing the agricultural ministry.

This was seen by some as an attempt by Moscow to preserve strained relations with countries in the global south whose food supplies have been deeply affected by the fallout from Russia’s decision to invade Ukraine.

Russia’s president Vladimir Putin has in recent weeks expressed unhappiness with the deal, claiming it was not benefiting the “poorest countries”.

However, the UN has not billed the agreement as intended to send grain directly to poorer nations, but one that made grain more accessible to all by lowering market prices.

Putin’s increased disapproval has also coincided with a series of military defeats for his forces, and the suspension of the deal comes as a counter-offensive in the southern Kherson region gathers pace.

“Why is Moscow disrupting the grain deal now? The answer is: Putin needs leverage as things go south for him on the battlefields in Ukraine, so the threat of global food crisis needs to be put back in the Russian toolbox of coercion and blackmail,” wrote Alexander Gabuev, senior fellow at the Carnegie Endowment for International Peace.

But he also warned the strategy could backfire: “The killing of the grain deal will create rifts between Russia and powerful players like Turkey and Saudi Arabia.”