Moscow’s military said ships targeted at their Crimean base were involved in the UN-brokered grain deal.
Russia had recently criticised the deal, saying its grain exports have suffered due to Western sanctions.
Russia’s decision “proves once again that negotiations with the Russian Federation are a waste of time”, a top Ukrainian official said.
“(Russian President Vladimir) Putin has turned food, the cold and prices into weapons against the world … Russia is waging a hybrid war against Europe, taking Africa and the Middle East hostage,” presidential aide Mykhailo Podolyak wrote on Twitter.
The UN also called for the preservation of the agreement.
“It is vital that all parties refrain from any action that would imperil the Black Sea Grain Initiative which is a critical humanitarian effort,” said Stephane Dujarric, spokesman for the UN secretary-general, underscoring the initiative was “having a positive impact” on food access for millions worldwide.
He said the UN chief’s office was in touch with Russian authorities over the issue.