President Vladimir Putin flew into Crimea yesterday for parades marking the Soviet victory in the second world war, his first visit since annexing the peninsula from Ukraine, which Russia says has been taken over by fascists.
Putin hailed Crimea's return to Russia as a "historic truth".
He told a cheering crowd in the port city of Sevastopol: "2014 will go down in history ... as the year when people living here firmly decided to be together with Russia, thus confirming their loyalty to historic truth."
The Russian leader added: "Much work remains, but we will overcome all difficulties ... because we are together. And that means we are even stronger."
In eastern Ukraine, where pro-Moscow rebels plan a referendum tomorrow to follow Crimea in breaking from Kiev, up to eight people were reported killed in the port of Mariupol, one of the bloodiest clashes yet between Ukrainian forces and separatists.
The head of Nato, locked in its gravest confrontation with Russia since the cold war, condemned Putin's visit to Crimea, whose annexation in March has not been recognised by Western powers. Secretary general Anders Fogh Rasmussen also renewed doubts over an assurance by Putin that he had pulled back troops from the Ukrainian border.
Earlier yesterday, Putin presided over the biggest Victory Day parade in Moscow for years. The passing tanks, aircraft and intercontinental ballistic missiles were a reminder to the world - and Russian voters - of Putin's determination to revive Moscow's global power, 23 years after the Soviet collapse.
"The iron will of the Soviet people, their fearlessness and stamina saved Europe from slavery," Putin said in a speech to the military and war veterans gathered in Red Square.
Ukraine's SBU security service accused Russian saboteurs of setting a fire that briefly disrupted state broadcasting services and the foreign ministry issued a statement describing Putin's visit as a deliberate escalation of the crisis.
In Mariupol, the main port on the Sea of Azov, a member of Ukraine's parliament said Ukrainian forces attacked the police headquarters in an attempt to drive out pro-Russian militants, and the building caught fire.
Oleh Lyashko said eight rebels had been killed in fighting. But Donetsk medical authorities said three had been killed in fighting and 25 wounded.
In Sevastopol, where Russia's Black Sea Fleet previously had to lease its base from Ukraine, servicemen and veterans marched in a parade before Putin's arrival that also included armoured vehicles and anti-aircraft missiles. Banners read "Sevastopol without fascists" and "It's our duty to remember".
In Slavyansk, the military stronghold of the separatists in eastern Ukraine, "people's mayor" Vyacheslav Ponomaryov and a guard of militiamen led a march of 2,000 people to lay flowers at a memorial to the war dead.
Voters will be asked tomorrow to approve the secession of self-styled "people's republics" in Donetsk and Luhansk.
Additional reporting by Agence France-Presse