Russia has warned there will be no extension of the Black Sea grain deal beyond May 18 unless the West removes barriers to its food and fertiliser exports.
"Without progress on solving five systemic problems there is no need to talk about the further extension of the Black Sea initiative after May 18," said the country's Foreign Ministry in a statement on Thursday.
The grain deal was brokered by the UN and Turkey last year amid rising prices and fears for global food security.
It allowed for the reopening of blockaded Black Sea ports, with Russia allowed to inspect cargoes.
Ukraine's ports can handle more grain than land routes, which are fraught with complications.
Russia has repeatedly demanded the removal of key obstacles to its exports, including the reconnection of Russian Agricultural Bank (Rosselkhozbank) to the Swift payment system.
Other demands include a resumption in supplies of agricultural machinery and parts; a lifting of restrictions on insurance and reinsurance; access to ports; the resumption of the Togliatti-Odesa ammonia pipeline; and the unblocking of assets and the accounts of Russian companies involved in food and fertiliser exports.
Russia agreed a short 60-day extension of the deal in March, in what Russia's Foreign Minister Sergey Lavrov described as a “small escalatory move” after the deal had previously operated for 120 days at a time.
“After we extended the deal for 120 days, we saw no indication that those issues could be solved and grew tired of appealing to the conscience of those who determine it,” Mr Lavrov said.
Ukraine is a top exporter of wheat, corn and sunflower oil.
The agreement has so far allowed the export of more than 25 million tonnes of grain and other agricultural products.