Ukraine's President Volodymyr Zelensky warned Sunday that Russian forces are preparing to shell Odessa, a historic port city on the Black Sea coast.
"They are preparing to bomb Odessa. Odessa!" he declared, in a video address. "Russians have always come to Odessa. They have always felt only warmth in Odessa. Only sincerity. And now what? Bombs against Odessa? Artillery against Odessa? Missiles against Odessa?" he demanded.
"It will be a war crime. It will be a historical crime."
Russian forces have made progress in southern Ukraine since their February 24 invasion, overrunning the city of Kherson and besieging the port of Mariupol, but Odessa has so far been largely spared.
Almost a million people live in Odessa, a cosmopolitan harbour on Ukraine's southern coast with both Ukrainian and Russian speakers and Bulgarian and Jewish minorities.
The Russian advance from occupied Crimea has in part turned east to link up with Russian-backed separatists and to seize the Azov Sea port of Mariupol.
But another part of the force has also headed west to Kherson, on the road towards Odessa. The city is also close to the Moldovan border and the Russian-occupied region of Transnistria.
During the first 11 days of the conflict, Russian forces from Belarus have also advanced on the capital Kyiv from the northwest and northeast, while another group bombarded the northern city of Kharkiv.
Several cities have been bombed and shelled and the UN estimates that more than a million civilians have been driven from their homes by the fighting.