Russia said it is suspending its participation in a UN-brokered agreement to export Ukrainian agricultural produce from three Black Sea ports.
Moscow is pulling out of the deal, the defence ministry said in a statement shared by state media outlet Tass, after what it called a terrorist attack on ships in Crimea.
The US, accusing Russia of “weaponising food”, and the EU led international condemnation of Russia’s move.
The UN-brokered deal came into effect in July after warnings that a halt in exports from Ukraine could lead to severe global food shortages and famine.
Several million tonnes of grain have been exported under the agreement, which was also brokered by Turkey.
Ukrainian Foreign Minister Dmytro Kuleba said Moscow was using “false pretexts” to block grain exports.
UN Secretary General Antonio Guterres on Sunday expressed "deep concern" that Ukraine's maritime grain exports were halted and pushed back his flight to an Arab League summit.
"The secretary general is deeply concerned about the ongoing situation regarding the Black Sea Grain Initiative," his spokesman said. "He has decided to delay his departure for the Arab League Summit in Algiers by a day to focus on the issue."
US Secretary of State Antony Blinken called the grain deal an “essential, life-saving initiative” that has seen more than 9 million tonnes of food shipped and helped bring down global prices.
“Any act by Russia to disrupt these critical grain exports is essentially a statement that people and families around the world should pay more for food or go hungry,” he said.
“In suspending this arrangement, Russia is again weaponising food in the war it started, directly affecting low and middle-income countries and global food prices, and exacerbating already dire humanitarian crises and food insecurity.”
The EU called on Russian leaders to change their decision and allow grain exports.
“Russia's decision to suspend participation in the Black Sea deal puts at risk the main export route of much needed grain and fertilisers to address the global food crisis caused by its war against Ukraine,” EU foreign policy chief Josep Borrell said.
“The EU urges Russia to [reverse] its decision.”
Turkey's Defence Minister Hulusi Akar was in talks with counterparts in Moscow and Kyiv to try to revive the grain deal, the ministry said on Sunday. He has asked everyone involved to avoid any "provocation".
A Russian-installed official in Crimea said that the Saturday morning drone attack on ships in Sevastopol — the largest city in Crimea — was the “most massive” on the peninsula since the invasion of Ukraine in February.
The attack involved “British specialists” and struck ships ensuring the security of the grain corridor, Moscow said.
Ukraine has accused Moscow of “blackmail” and “invented terror attacks” following Russian claims Kyiv was responsible.
Ukrainian President Volodymyr Zelenskyy said it showed “an absolutely transparent intention of Russia to return the threat of large-scale famine to Africa and Asia”.
Before the invasion, Russia and Ukraine together accounted for about a third of global wheat exports.
UN authorities are in contact with Moscow following the announcement, spokesman Stephane Dujarric said.
“It is vital that all parties refrain from any action that would imperil the Black Sea Grain Initiative, which is a critical humanitarian effort that is clearly having a positive impact on access to food for millions of people around the world,” he said.
Russian Agriculture Minister Dmitry Patrushev said on Saturday that Moscow was ready to supply up to 500,000 tonnes of grain to poor countries in the next four months for free, with assistance from Turkey, and supplant supplies of Ukrainian grains.
“Taking into account this year's harvest, the Russian Federation is fully prepared to replace Ukrainian grain and deliver supplies at affordable prices to all interested countries,” he said.