President Vladimir Putin took a victory lap Friday in his first visit to Crimea since its annexation by Russia, as fighting in eastern Ukraine left 21 dead just days ahead of a separatist vote.
The visit drew a sharp rebuke from authorities in Kiev, who accused the Russian strongman of stoking tensions with his visit to Sevastopol, home to Russia's Black Sea fleet.
"This provocation once again confirms that Russia deliberately seeks further escalation of tensions," the ministry said, calling the visit a "flagrant violation of Ukraine's sovereignty".
The White House also condemned the trip, with National Security Council spokesman Laura Magnuson saying it "will only serve to fuel tensions".
With unease high ahead of an independence vote planned for Sunday in parts of eastern Ukraine, fighting between Ukrainian troops and pro-Moscow militants erupted in the southeastern port city of Mariupol.
Interior Minister Arsen Avakov said on his official Facebook page that the fighting had killed 20 insurgents and one police officer. Five policemen were also wounded and four rebels captured.
An AFP reporter in the city said its police headquarters were a gutted wreck, with parts of the building on fire as firefighters struggled to douse the blaze.
"The tanks came and shot at the building," said one eyewitness who gave his first name as Aleksandr.
"There was an awful lot of shooting," he said. "I loaded one young man with a head wound into a taxi -- I don't know if he survived or not."
In Sevastopol, Putin reviewed Russian ships in the bay, hailing the sailors on board with a "Hello comrades!" as he congratulated them on Friday's 69th anniversary of the Soviet victory over the Nazis in World War II.
Putin said 2014 "will go down in history" as the year when the "historic truth" of Crimea as part of Russia was recognised.
"Much work remains ahead, but we will overcome all difficulties... because we are together. And that means we are even stronger," Putin told a cheering crowd.
Russia's annexation of Crimea in March set off the worst diplomatic crisis in the West's relations with Moscow since the end of the Cold War.
It has been followed by uprisings and fighting in eastern Ukraine that have raised concerns of a civil war erupting on Europe's doorstep.
Despite a surprise call from Putin this week to delay independence referendums, rebels holed up in more than a dozen towns and cities in eastern Ukraine vowed to press ahead with votes this Sunday that are bound to increase tensions.
Putin flew to Sevastopol after overseeing the traditional Victory Day parade in Moscow's Red Square.
Addressing some 11,000 troops who marched alongside tanks, armoured vehicles and mobile missile systems, Putin hailed Russia's "all-conquering patriotic force".
The Soviet Union's victory over Nazi Germany 69 years ago has long been a source of great pride throughout the ex-USSR, which lost some 30 million citizens during World War II.
In contrast to the display of military hardware on Red Square, Ukraine held muted Victory Day celebrations in a bid to avoid violence.
The head of Kiev's city council banned large-scale public gatherings or parades in the capital, fearing that the veterans could be attacked by "Russian provocateurs".
A short ceremony was held in the presence of Prime Minister Arseniy Yatsenyuk, several former presidents and a few dozen veterans in the city's main park.
Their chests bulging with medals, the veterans marched with flowers in their hands but the atmosphere was subdued.
"Today's celebration has been ruined. We cannot celebrate the victory as usual because of the political situation," said one of the veterans, Vasyl Kupshenko.
Violence in Ukraine in recent weeks has seen 14 troops killed, three helicopter gunships downed and 66 servicemen injured in assaults on the rebels. The fighting has also claimed the lives of more than 30 insurgents.
Clashes that resulted in a horrific inferno in the southern port city of Odessa last week claimed another 42 lives, most of them pro-Russian activists.
The crisis kicked off after the ouster of the country's pro-Kremlin president Viktor Yanukovych in February and the West is counting on a presidential election on May 25 to stem the chaos.
The violence has prompted many Western politicians to warn that the country of 46 million people is slipping towards a civil war that would imperil peace in Europe.
Accusing Russia of backing pro-Moscow militants, the United States and European Union have imposed a series of sanctions on Putin and his inner circle. EU ministers are to meet on Monday to consider further measures.
Officials from the EU, Russia and Ukraine are also set to meet in Brussels on Monday for further talks on the future of Russian gas supplies to Kiev and Europe.
Europe is desperately worried after Russia ordered Ukraine to pay up front for all its natural gas deliveries, raising the spectre of imminent shortages for the EU.
Nearly 15 percent of Russian gas consumed by the 28-nation bloc transits though Ukraine.