The 120-day Black Sea Grain Initiative, a UN-led deal agreed with Moscow and Kyiv, runs out on November 19.
A report by the UN's trade and development agency UNCTAD called its extension "critical."
The deal helped push down historically high market prices, but they are rising again amid concerns about whether the initiative will be renewed.
UNCTAD claimed that without the renewal there was little hope for providing food security, especially in the least-developed countries where nearly 20 percent of the wheat exports have gone.
The UN would like to extend the agreement for one year. but Russia is unhappy with some aspects of the arrangements and how they work, fueling doubt as to whether the Kremlin would want to continue.
Gennady Gatilov, Russia's ambassador to the UN in Geneva, said Thursday that little had been achieved in the latest negotiations over the deal's future.
"The extension of the deal depends on ensuring full implementation of both previously-reached agreements," he said.
Two agreements brokered by the UN and Turkey were signed on July 22 -- to allow the export of Ukrainian grain blocked by Russia's war in the country, and the export of Russian food and fertilizers despite Western sanctions imposed on Moscow.
Russia, a world grain power, complains that it cannot sell its production and its fertilizers due to Western sanctions.
In discussions with the UN, "we have emphasized our concerns about the implementation of the Russian part of the deal, because we are still experiencing troubles with essential logistics," Gatilov added.