A proposal by U.N. chief Antonio Guterres on improving and extending a deal on the safe Black Sea export of Ukrainian grain can succeed only if the international community collectively pressures Russia, a senior Ukrainian official said on Tuesday.

Guterres, the U.N. secretary-general, set out proposals for a "way forward aimed at the improvement, extension and expansion" of the agreement in a letter to Russian President Vladimir Putin.

"Guterres' absolutely justified initiative can succeed only if the international community collectively pressures Russia," Ukrainian Presidential adviser Mykhailo Podolyak said in written comments to Reuters.

"Ukraine, on the other hand, will continue to follow the agreements with Turkey and the U.N. and will continue to deliver grain cargoes to their destination, solving the problem of global food supply," he added.

The Kremlin said on Tuesday that a global shortfall in food supplies was not primarily attributable to a lack of Russian and Ukrainian grain on the market.

It also restated its position that provisions relating to Russian grain exports had not been properly implemented.

Moscow has signaled it will not allow the grain initiative, which was signed last July and lifted a blockade of three Ukrainian Back Sea ports following Russia's invasion, to continue beyond May 18 because it says a list of demands for its exports has not been met.

Podolyak also denied an assertion by Russia's defense ministry that Kyiv was trying to attack its ships in the Black Sea, actions which it said threatened prospects for the extension of the grain export deal.