President Vladimir Putin flew in to Crimea on Friday for parades marking the Soviet victory in World War Two, his first visit since annexing the peninsula from a Ukraine that Russia says has been taken over by fascists.
In east Ukraine, where pro-Moscow rebels plan a referendum on Sunday 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. He also renewed doubts over an assurance by the Kremlin leader that he had pulled back troops from the Ukrainian border.
The government in Kiev called Putin's visit a "provocation" that was intended deliberately to escalate the crisis.
Earlier on Friday, 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 on Red Square.
He was expected to attend a military parade and other war anniversary events in Crimea. This year is also the 70th anniversary of the battle in which the Red Army won back control of the Black Sea peninsula from the Nazis.
Putin is sure to receive a hero's welcome in the port of Sevastopol, where Russia's Black Sea Fleet is based.
But NATO Secretary-General Anders Fogh Rasmussen said: "His visit to Crimea is inappropriate."
The head of the U.S.-led defence pact was speaking in formerly Soviet Estonia, one of a host of east European nations that joined after the collapse of communism, seeking refuge from the power of Moscow, which many in the region regarded as having enslaved them following its victory in World War Two.
Ukrainian Prime Minister Arseny Yatseniuk, in office since an uprising overthrew the Kremlin-backed elected president in Kiev in February, rejects Russian allegations that his power is the result of coup backed by neo-Nazi Ukrainian nationalists.
"Sixty-nine years ago, we, together with Russia, fought against fascism and won," he said after a Victory Day church service in the capital. Now, he added, "history is repeating itself but in a different form".
Where Russia and Ukraine stood shoulder to shoulder in the past against Germany, now Germany was "standing shoulder to shoulder with us", along with the United States and Britain.
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 a dramatic and apparently conciliatory gesture, Putin urged the Ukrainian separatists on Wednesday to call off the secession referendum they plan in the Russian-speaking eastern industrial regions of Donetsk and Luhansk. But they plan to go ahead. Moscow insists it has no direct control over the armed militants, despite assertions to the contrary from Kiev.
In Mariupol, the region's 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.
Interfax-Ukraine news agency said eight people were killed.
But Donetsk medical authorities said three had been killed in fighting and 25 wounded.
A local photographer at the scene told Reuters the building was ablaze and that two bodies were lying in the street outside.
"One of them is definitely a police officer," he said.
A fire a week ago during clashes in the southwestern port of Odessa killed dozens of pro-Russian activists, hardening attitudes in the east against the Kiev authorities.
Tetyana Ignatchenko, a journalist in Mariupol, said there was fierce fighting outside the police headquarters. Ukrainian forces brought several armoured vehicles into the town, a major industrial centre with a population of about half a million.
Local media said separatists had seized a tank in the centre of town and built barricades around the city.
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".
"I'm here to prevent any provocations from the fascists. I served in a self-defence unit during March, and I consider it my duty to be here," said Natalya Malyarchuk, 52, a resident of Sevastopol, wearing a red arm band saying "Patrol."
The ethnic Russian majority among Crimea's two million population broadly welcomed the Russian takeover that came in the wake of the Kiev uprising. Given by Soviet leaders to Ukraine only in the 1950s, many Russians long saw it as rightfully theirs. Western powers have imposed sanctions against Russia in response, but reactions have been muted.
While Putin's redrawing of European borders has sparked great alarm across the continent, U.S. and European leaders are concerned not to harm their own economies by isolating Moscow.
And there is little popular support in the West for an armed conflict with Russia on behalf of Ukraine, a country that is not a member of NATO and where successive leaders have left a legacy of massive corruption, poverty and feeble state institutions.
In Sevastopol, factory worker Vasily Topol, 31, wearing a white T-shirt with an image of Putin in sunglasses and the words "Russia's Army", said life was better since becoming Russian.
"We have the greatest admiration for Putin, we are morally and materially better off since Crimea became part of Russia," he said, speaking on an embankment overlooking Russian warships.
"My salary has risen by two and a half times."
In Slaviansk, the military stronghold of the separatists in eastern Ukraine, separatist "people's mayor" Vyacheslav Ponomaryov and a guard of militiamen led a march of around 2,000 people to lay flowers at a memorial to the World War Two dead.
Veteran Anatoly Strizhakov said: "Look at all these people - the children, the women, the pensioners. We're all here, ready for anything ... Today shows we've got the spirit to stand up to whatever the Ukrainians are planning."
Ponomaryov, who fired a pistol three times in the air during the ceremony, reassured people it would be safe to vote on Sunday. Larissa Kurennaya said of the veterans to whom she was giving lilac and red carnations under a statue of Lenin:
"They are a reminder that war must be avoided at all costs ... We will never surrender to the Ukrainians but this referendum could help resolve the situation peacefully.
"I'm voting for the republic and so is everyone I know."
Voters in the two regions, with a combined population of over 6 million, will be asked to vote Yes to the secession of self-styled "People's Republics" in Donetsk and Luhansk.
Opinion polls in recent months have indicated that support for such a move is far from solid and it is unclear how many people will actually take part in voting. A referendum in Crimea in March, which many boycotted, backed secession by 97 percent.
As he headed to the parade in Slaviansk, his blue uniform weighed down by Soviet medals, 86-year-old veteran Alexander Fyodorovich, said: "There's not much cause for celebration.
"The Ukrainians are at the gates and there are barricades on almost every road in town. I just want peace - I don't care about Ukrainians, Russians or anything.
"We need to sort this out without more bloodshed."