Russian President Vladimir Putin (R) and Turkish President Recep Tayyip Erdogan attend a meeting in Sochi. AFP
Both Ukraine and Russia have aired rival plans to start sending grain across the Black Sea on their own.
But Erdogan, who helped broker the original deal, has been trying to revive the agreement and use it as a basis for broader peace talks.
"The alternative proposals brought to the agenda could not offer a sustainable, secure and permanent model based on cooperation between the parties like the Black Sea Initiative," Erdogan said at a joint media appearance with Putin in Sochi.
Ukraine has sent four ships along a new sea route, while Russia is preparing a plan to send foodstuffs for free to some African countries, and to send discounted grain for processing in Turkey under a deal also including Qatar.
Erdogan said on Monday that Turkey and the United Nations had prepared new proposals aimed at addressing Russia's problems with the deal, adding that he hoped to reach a workable solution "soon".
"We have prepared a new proposal package in consultation with the UN. I believe that it is possible to get results. I believe that a solution that will meet Turkey's expectations will be reached soon," Erdogan said.