The United Kingdom is working closely with Türkiye on restoring the landmark deal that allowed Ukraine to export grain safely from its seaports despite Russia’s invasion, Prime Minister Rishi Sunak said Tuesday.

The remarks came during Sunak's phone call with Ukrainian President Volodymyr Zelenskyy, during which the pair agreed on the importance of ensuring Ukraine can export grain to international markets, the prime minister’s office said.

"The prime minister said the U.K. was working closely with Türkiye on restoring the grain deal, and we would continue to use our role as chair of the U.N. Security Council to further condemn Russia’s behavior," a spokesperson for Sunak said in a statement.

Russia last week quit the Black Sea Grain Initiative, brokered by the United Nations and Türkiye last July, aimed at helping prevent a global food crisis by allowing grain blocked by the war in Ukraine to be safely exported. It said demands to improve its own food and fertilizer exports had not been met, and that not enough Ukraine grain had reached the poorest countries.

The Kremlin on Tuesday reiterated it was impossible for Moscow to return to the deal until an agreement related to Russian interests was honored.

Its statement came a day after U.N. Secretary-General Antonio Guterres urged Russia to rejoin the initiative, in line with a proposal he had made to Russian President Vladimir Putin.

"With the termination of the Black Sea Initiative, the most vulnerable will pay the highest price," Guterres told the U.N. Food Systems summit in Rome on Monday. "When food prices rise, everybody pays for it."

But the Kremlin suggested Guterres' proposal did not address its main complaint: There had been no progress on a related agreement that was designed to facilitate Russian food and fertilizer exports amid Western sanctions imposed in response to the war.

"Indeed, Mr. Guterres' letter again set out some kind of action plan and contained promises that at some point it would be possible to implement the Russian part of these arrangements," Kremlin spokesperson Dmitry Peskov told reporters.

"Unfortunately, at the moment it is impossible to return to the deal because it (the Russia-related agreement) is not being implemented, and de facto it has never been implemented."

Guterres had written to Putin on July 11 in a final effort to save the deal. He proposed Russia extend it – with a daily limit of four ships traveling to Ukraine and four ships leaving – in return for connecting a subsidiary of Russia's Agricultural Bank, Rosselkhozbank, to the SWIFT global payments system.

A key demand by Moscow has been reconnecting Rosselkhozbank to SWIFT. The European Union cut it off in June 2022.

Peskov said Putin had made it clear that Moscow would be ready to revive the deal when the memorandum related to Russia was fulfilled.

Ukraine and Russia are both leading grain exporters. Russia's grain exports have risen since the war, but its ammonia and potassium-based fertilizers have fallen sharply.

"I remain committed to facilitating the unimpeded access to global markets for food products and fertilizers from both Ukraine and the Russian Federation and to deliver the food security that every person deserves," Guterres said Monday.

After quitting the deal, Moscow said it would consider cargo ships traveling to Ukraine through the Black Sea as potential military targets. Since then, it has been pounding Ukrainian food-exporting ports nearly on a daily basis.

Sunak on Tuesday also told Zelenskyy he was appalled by the devastation caused by the recent Russian attacks on the port city of Odessa, the statement said.