United Nations Secretary-General Antonio Guterres is still waiting for a response from Russian President Vladimir Putin on a proposal to extend a deal allowing the safe Black Sea export of Ukraine grain beyond Monday, a UN spokesperson said on Friday.

Guterres wrote to Putin on Tuesday asking him to extend the Black Sea deal in return for connecting a subsidiary of Russia's Agricultural Bank (Rosselkhozbank) to the international payment system SWIFT, sources told Reuters.

The last ship traveling under the Black Sea deal is loading its cargo at Ukraine's Odesa port. Russia has not agreed to register any new ships since June 27 and the initiative will expire on Monday if Moscow does not agree to extend it.

Russia has threatened to quit the deal - brokered by the UN and Turkey in July 2022 - because Moscow has said its demands to improve its own grain and fertilizer exports have not been met. Ukraine and Russia are among the world's top grain exporters.

More than 32 million metric tons of corn, wheat and other grains have been exported by Ukraine under the arrangement. Russia has complained that not enough has reached poor countries, but the UN has argued that it has benefited those states by helping lower food prices more than 20 per cent globally.

"Discussions are being had, WhatsApp messages are being sent, Signal messages are being sent and exchanged. We're also waiting for a response to the letter," UN spokesman Stephane Dujarric told reporters when asked about negotiations.

Russia has not made any statements on the extension of the Black Sea grain deal, the Kremlin said on Friday after Turkish President Tayyip Erdogan earlier caused confusion when he said that he was in agreement with Putin that it should be extended.

According to TASS news agency, Putin said on Thursday he had not seen the letter from Guterres proposing an extension of the deal, but that Russia was in contact with UN officials.

UN Secretary of State Antony Blinken on Friday pushed for Russia to extend and expand the Black Sea deal, accusing Russia of using the agreement "as a weapon" by threatening to end it.

"If Russia is not going to end its horrific war of aggression against Ukraine, at the very least it could extend the Black Sea Grain Initiative so that these food products can get out to the world, keeping prices down, keeping supply up," Blinken told a news conference in Jakarta.

To convince Russia to agree to the Black Sea deal, a three-year memorandum of understanding was struck in July 2022 under which UN officials agreed to help Russia get its food and fertilizer exports to foreign markets.

While Russian exports of food and fertilizer are not subject to Western sanctions imposed after the invasion of Ukraine, Moscow has said restrictions on payments, logistics and insurance have amounted to a barrier to shipments.

A key demand by Russia is the reconnection of Rosselkhozbank to SWIFT. It was cut off by the EU in June 2022 over Russia's invasion of Ukraine in February 2022. The EU is considering connecting a Rosselkhozbank subsidiary to SWIFT to allow for grain and fertilizer transactions, sources familiar with discussions said on Wednesday.