Sailing into this Black Sea port Friday amid a jubilant spectacle of fighter jets and warships, President Vladimir Putin celebrated the return of Crimea to Russia as "historic justice" during a Victory Day display of military pomp and patriotism.

The gravity of the crisis gripping the rest of Ukraine was underscored by deadly clashes in the east, where fighting left bodies in the streets of the seaside city of Mariupol and the police station a smoldering ruin.

At least seven people were killed and dozens injured in the city, one of at least a dozen where pro-Russian insurgents are agitating to follow Crimea's lead in seceding from Ukraine.

Speaking before a cheering crowd of thousands on a triumphant first visit to Crimea since its annexation into Russia, Putin hailed the incorporation of its 2 million people as a "return to the Motherland" and a tribute to the "historical justice and the memory of our ancestors."

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A Russian serviceman aboard salutes next to the Crimean flag, during the Victory Day parade in Moscow's Red Square. Russian President Vladimir Putin has overturned decades of post-Cold War diplomacy by proclaiming the right to send troops to Ukraine and seizing and annexing Crimea. (Grigory Dukor/Reuters)

The Russian leader's visit to the Crimean port of Sevastopol, where Russia's Black Sea Fleet is based, came on Victory Day, which commemorates the defeat of Nazi Germany and is Russia's most important holiday. The trip was strongly criticized by the United States, NATO and Ukraine's Foreign Ministry, which said it trampled on Ukraine's sovereignty and international law.

Putin's two Victory Day celebrations — a massive show of military muscle in the annual Red Square parade in Moscow, followed by the extravaganza in Sevastopol — rubbed salt in the wounds of Ukraine's interim government in Kyiv without ever once mentioning its name.

In Sevastopol, Putin rode a cabin cruiser-type boat past hulking warships, issuing greetings to their crews, as warplanes and helicopters swooped over the vast harbor. He then stepped onto land for a short address to the tens of thousands on the shore who came to watch the spectacle.

He expanded on the theme of righting a historic wrong with Crimea's return to Russia in a later address at a commemorative concert, saying Moscow respected other countries' interests and "we ask that all of them show regard for our legal interests, including the restoration of historical justice and the right to self-determination."

Increasing unrest in eastern Ukraine

Conquered by Russia in the 18th century under Catherine the Great, Crimea only became part of Ukraine in 1954 when Soviet leader Nikita Khrushchev transferred jurisdiction from Russia. The move was a formality until the 1991 Soviet collapse meant Crimea landed in an independent Ukraine. It remained under Ukrainian control until its annexation by Russia in March, following a hastily arranged referendum — moves condemned by the West and Kyiv.

The violence in the strategic port of Mariupol on the Azov Sea — along the main road between the Russian border and the Crimean Peninsula — was a clear sign of increasing unrest in eastern Ukraine.

The Donetsk region, which includes Mariupol, and the neighbouring Luhansk region are to hold a hastily organized referendum Sunday on declaring sovereignty, a move likely to deepen the crisis between supporters of Ukraine's fledgling government and pro-Russia insurgents who claim the authorities in Kyiv are a fascist junta.

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Russian servicemen march in Moscow's Red Square during the Victory Day parade, which included a marine unit from the Black Sea Fleet that flew the Crimean flag on its armoured personnel carriers. (Sergei Karpukhin/Reuters)

There were varying accounts of Friday's violence in the city of a half-million people that also was hit by unrest last month.

Ukrainian Interior Minister Arsen Avakov said about 60 gunmen attacked the Mariupol police station and were repulsed in an operation that killed one policeman and about 20 people he called "terrorists."

The Donetsk regional government said seven people were killed and 39 others were wounded. The conflicting death tolls could not be reconciled. An Associated Press reporter saw three bodies in the street — one of them covered by a blanket with a policeman's hat placed at the head.

As the police station burned, residents gave accounts of the day's events that contradicted the official line. Some said government troops fired on unarmed protesters and attacked police who were protecting demonstrators occupying the nearby administration headquarters.

Amateur video showed soldiers firing warning shots and later wounding men who angrily confronted them. At least one man in civilian clothes could be seen shooting in the direction of the soldiers, who backed away on foot.

Larissa Gremacheva, a retiree, said soldiers fired on unarmed men.

"They began to shoot, and with my own eyes I saw how one man was wounded in his leg and another in his arm," she said.

'Provocative and unnecessary'

Government troops appeared to have lost an armoured personnel carrier to attacking mobs. By nightfall, all government forces had abandoned the city centre, which was blocked off with barricades of tires.

U.S. State Department spokeswoman Jen Psaki condemned the violence, which she said was "caused by pro-Russia separatists."

"We continue to call for groups who have jeopardized public order by taking up arms and seizing public buildings in violation of Ukrainian law to disarm and leave the buildings they have seized," she said.

Meanwhile, the Obama administration and NATO Secretary General Anders Fogh Rasmussen condemned Putin's visit to Crimea.

"We still consider Crimea as Ukrainian territory and from my knowledge the Ukrainian authorities haven't invited Putin to visit Crimea, so from that point of view his visit to Crimea is inappropriate," Fogh Rasmussen told reporters in Tallinn, Estonia.

Psaki called the trip "provocative and unnecessary."

Earlier, in Moscow, Putin watched as about 11,000 Russian troops marched across Red Square to the tunes of marches and patriotic songs. They were followed by columns of dozens of tanks and rocket launchers as some 70 combat aircraft, including giant nuclear-capable strategic bombers, roared overhead. 

In a dig at Ukraine, the parading troops on Red Square included one marine unit from the Black Sea Fleet that flew the Crimean flag on its armoured personnel carriers.

No evidence of Russian pullback

The West and the Ukrainian government accuse Russia of fomenting the unrest in Ukraine's east, where insurgents have seized government buildings in a dozen cities and towns.

The referendum on independence being held Sunday in the Donetsk and Luhansk regions — an area that encompasses 6.5 million people — is similar to the plebiscite that paved the way for Moscow's annexation of Crimea.

Putin's surprise call Wednesday for the rebels to delay the vote appeared to reflect Russia's desire to distance itself from the separatists as it bargains with the West. But insurgents in Ukraine's Russian-speaking east defied Putin's call and said they would go ahead anyway.

Putin also said Russia had withdrawn its forces from the Ukrainian border, but the Pentagon and NATO said there was no evidence of a pullback.

"We still don't have visible evidence of Russian withdrawal of troops from Ukraine's border," Fogh Rasmussen told reporters Friday. "I would be the first to welcome it if Russian troops were pulled out."

Russia wants Ukraine to adopt a new constitution that would give broad powers to its regions, helping Moscow to keep the country's east in its orbit. It also has sought guarantees that Ukraine would not join NATO. Ukraine has rejected the Russian demands.

The head of the Organization for Security and Co-operation in Europe, Lamberto Zannier visited Kyiv on Friday and criticized the referendum in the east, calling it a "divisive initiative."

The United States and the European Union have slapped travel bans and asset freezes on members of Putin's entourage in response to the annexation of Crimea.

Despite the sanctions, Putin is set to travel to France in early June for a ceremony marking the 70th anniversary of the D-Day invasion that hastened the end of the Second World War, his first encounter with Western leaders since the start of the Ukrainian crisis.