Moscow has accused Ukraine of attacking a vital bridge that links Russia and Crimea. However, the Kremlin has said there is no link between the attack and the decision to pull out of the deal.
UN Secretary-General Antonio Guterres said Russia's decision to exit the Black Sea grain deal will "strike a blow to people in need everywhere."
Guterres said the agreement had until now "been a lifeline for global food security and a beacon of hope in a troubled world."
"Ultimately, participation in these agreements is a choice," he told reporters in New York City.
"But struggling people everywhere and developing countries don't have a choice. Hundreds of millions of people face hunger and consumers are confronting a global cost-of-living crisis. They will pay the price"
The UN Secretary-General also said he was "deeply disappointed" that his letter to Russian Vladimir Putin that contained a proposal to save the agreement went unheeded.