Kyiv said Wednesday that work had resumed at three Black Sea ports designated under a recent deal with Russia to resume cereals' exports that have been blocked by Russia's invasion.

"In connection with the signing of the agreement on the unblocking of Ukrainian ports for the export of grain, work has resumed in the ports of Odessa, Chernomorsk and Pivdennyi," the Ukrainian navy said in a statement on social media.

Kyiv and Moscow last week agreed a mechanism with the help of Turkey and the United Nations to allow blocked Ukrainian grain to be exported from the three ports.

Ukraine said Monday that some exports could restart as early as "this week".

The navy said in its statement that when exports do resume, cargo ships will be escorted to and from the ports.

"The entry and exit of ships to seaports will be carried out by forming a convoy that will accompany the lead ship," it said in the statement, adding that safe routes were still being determined.

Russia and Ukraine are major exporters of agricultural products, but Moscow's invasion has severely disrupted Ukrainian wheat exports as the fighting damaged harvests and left ports blocked and mined.