Ukraine battles to hold eastern bastions

Ukrainian forces braced Sunday to defend their final bastion in the devastated port city of Mariupol, desperate to deny Russia a symbolic win on the eve of Moscow's Victory Day celebrations.

Shelling and missile strikes have intensified in the build up to the World War II anniversary, and rescuers are searching for 60 Ukrainian civilians feared killed in the bombing of a village school.

President Volodymyr Zelensky marked the anniversary on the end of the World War by comparing Ukraine's battle for national survival to the region's war of resistance against its former Nazi occupiers.

"Decades after World War II, darkness has returned to Ukraine, and it has become black and white again," Zelensky said, in a monochrome social media video shot against the backdrop of a bombed out apartment block.

Russia, meanwhile, was gearing up for a Victory Day parade designed to associate the invasion of its neighbour with the national pride felt over the Soviet Union's defeat of Germany. 

"Today, our soldiers, as their ancestors, are fighting side by side to liberate their native land from the Nazi filth with the confidence that, as in 1945, victory will be ours," Putin said.

Zelensky was also to meet G7 leaders via video conference to discuss the crisis, and European diplomats will meet again next week to hammer out the details of their latest sanctions package against Moscow.

On the ground, the key battles were being fought in Ukraine's east.