Russia and Ukraine both say the deal was brokered by the United Nations and Turkey in July.

There was no immediate comment on the allegation, levelled by Russia's Foreign Ministry, from Ukraine which has blamed Moscow for problems with the agreement. Moscow did not immediately provide documentary evidence to back its assertion.

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Russia and Ukraine both say the deal, brokered by the United Nations and Turkey in July, is in danger of collapsing just as Poland, Hungary and Slovakia have imposed import bans on Ukrainian grain.

Russia has repeatedly warned it will not renew the deal beyond May 18 unless the West agrees to lift a host of restrictions on payments, logistics and insurance which it says are hindering its own agricultural exports.

The Marshall Islands-flagged bulk carrier Riva Wind is seen at the seaport in Odesa. File/Reuters

Russian Foreign Ministry Spokeswoman Maria Zakharova said in a statement that the Joint Coordination Centre (JCC) in Istanbul, which oversees the deal, was experiencing difficulties with the registration of new vessels and inspections.

The problems were caused "solely as a result of the actions of Ukrainian representatives, as well as U.N. representatives, who, apparently, do not want or cannot resist them," she said.

In the same statement, Zakharova accused Ukraine of "trying to exploit the 'Black Sea initiative' as much as possible, not refraining from abuses of the rules of procedure or demands for bribes from ship owners. All for the sake of maximizing commercial profits."

Ship owners who refused to pay a bribe to Ukrainians were forced to wait for more than a month while they waited for registration, she said.

And Russian proposals to add vessels carrying grain to African countries in need had been "met with hostility" by Ukrainian representatives, she said, who then stopped inspections for 27 outgoing ships carrying 1.2 million tonnes of cargo.

"The calculation is simple — to launch a propaganda machine with the help of Westerners and the United Nations and again 'play the food card'," Zakharova said.