"Exports would take place through three ports: Odessa, Pivdennyi and Chornomorsk. But in the future we hope we could expand them," Ukrainian lawmaker Rustem Umerov told reporters.
He added that the safety of the shipments would be overseen by a UN monitoring group based in Istanbul.
Umerov also said that Russian ships should not be allowed into Ukrainian waters as part of the anticipated agreement.
"We do not trust them, even if they sign an agreement with the UN. This is an aggressor country," he said.
Ukraine and Russia have held talks under Turkish and UN mediation to unblock crucial grain exports and ease a food crisis that has sent global food prices soaring.
Up to 25 million tonnes of wheat and other grain have been blocked in Ukrainian ports by Russian warships and landmines Kyiv has laid to avert a feared amphibious assault.
The first direct talks between the warring sides' military delegations since March -- attended in Istanbul last week by Turkish and UN officials -- came up with an initial draft for resolving the impasse.
The sides were meant to have met again this week for the possible signature of a formal agreement.
But no talks had been confirmed by Thursday and new demands from Moscow put the prospects of an imminent deal in doubt.
