Russian President Vladimir Putin told Turkish leader Recep Tayyip Erdogan Tuesday that he wanted "real guarantees" from Kyiv before it potentially rejoined the grain deal.
Putin told Erdogan in a phone call that Russia sought "real guarantees from Kyiv about the strict observance of the Istanbul agreement, in particular about not using the humanitarian corridor for military purposes", according to a statement from the Kremlin.
The Turkey and UN-brokered deal allowed Ukrainian grain exports to resume in August, easing a food crisis caused by the conflict.
On Saturday Russia accused Ukraine of misusing the safe shipping corridor for an attack on Russian ships in Crimea and suspended its participation in the agreement.
Putin told Erdogan "it is necessary to conduct a thorough investigation into the circumstances of the incident" against the Black Sea fleet.
"Only after that will it be possible to consider the question of resuming work" within the deal, the Kremlin statement said, referring to both the investigation and guarantees it is seeking.
For the second time in as many days Russian Defence Minister Sergei Shoigu discussed the deal with his Turkish counterpart Hulusi Akar on Tuesday, the Russian defence ministry said.
Ukraine has said Russia's claim was a "false pretext" to withdraw from the deal.
On Tuesday more cargo ships left Ukrainian ports despite Russia warning a day earlier that it was "more risky, dangerous" to continue the exports without Russia's participation.