Ukraine has started online talks with partners on extending the Black Sea Grain Initiative aimed at ensuring Kyiv can keep shipping grain to global markets, a senior Ukrainian government source said on Tuesday.

The source said Ukraine had not held discussions with Russia, which blockaded Ukrainian Black Sea ports after its invasion last year, but that it was Kyiv's understanding that its partners were talking to Moscow.

The Black Sea Grain Initiative was brokered by the United Nations and Turkey last July and was extended in November. It is due to expire on March 18 unless an extension is agreed. (Reporting by Pavel Polityuk, Editing by Timothy Heritage)