Thousands of pro-Russian protesters assaulted Odessa's police headquarters yesterday, days after deadly clashes and a fire there killed dozens of their comrades in what Kiev said was a Russian plot to "destroy Ukraine".
The unrest in the southern port city threatened a new front in the Ukrainian government's battle against pro-Moscow militants, with an expanded military operation under way in the east against gunmen holding more than a dozen towns.
Prime Minister Arseniy Yatsenyuk said Russia was executing a plan "to destroy Ukraine and its statehood".
Watch: Deadly gunbattle at Ukrainian checkpoint
He was in Odessa to observe mourning for the 42 people who died there in clashes and the fire on Friday - most of them pro-Russian militants.
The unrest shaking the Black Sea city of 1 million people, he said, aimed "to repeat in Odessa what is happening in the east of the country".
In an effort to head off any retribution on the streets for Friday's bloodshed, Yatsenyuk sacked Odessa's police chiefs and ordered an inquiry.
The under-attack police in the headquarters also released some of the 150 pro-Russian militants arrested in Friday's clashes.
Although Moscow has admitted sending troops into Crimea ahead of annexing the strategic peninsula in March, it denies having a hand in Ukraine's unrest in the east and in Odessa.
Instead it blames the Kiev government and its Western backers for the carnage.
Kiev said the violence was provoked by foreign demonstrators sent in from Transnistria, a nearby breakaway pro-Russian region of Moldova where Moscow has a military garrison. It said most of the dead who had been identified so far were from there.
Moscow has also demanded a halt to the Ukrainian military offensive in the east, saying it has received "thousands" of calls for help from the population there for it to intervene.
Tens of thousands of Russian troops have been parked on Ukraine's border for two months, ready for an invasion Russian President Vladimir Putin says he has a right to launch - but "hopes" he won't have to.
Ukrainian officials have pushed on regardless with the operation, determined to crush the pro-Kremlin rebels.
The three-day death toll from the eastern offensive meanwhile stood at 10 at least as soldiers confronted gunmen in towns around the rebel bastion of Slavyansk.
Witnesses near the eastern town of Kostyantynivka saw a pro-Russian checkpoint abandoned and smouldering while barricades were hastily erected in the centre.
Rebels defending Kostyantynivka said there had been fighting overnight near the town's television tower.
But in the centre of besieged Slavyansk - whose outskirts saw fierce gun battles on Saturday - the situation was relatively calm. Some of its 160,000 citizens reported increasing difficulty obtaining basic foodstuffs.
Sporadic fighting was also reported in the eastern city of Lugansk and the port of Mariupol.
In annexed Crimea there were clashes between police and 2,000 pro-Kiev Tatars demonstrating against Russia's refusal to allow their leader Mustafa Dzhemilev into the peninsula.
Additional reporting by Reuters