President Vladimir Putin on Tuesday vowed Russia's military would be victorious in Ukraine and blamed Western countries for the conflict, comparing the fighting to World War II during a military parade on Red Square.

But his defiant address was overshadowed by scathing comments by Yevgeny Prigozhin, the head of the pro-Kremlin Wagner mercenary group, who accused Russia's military of repeated failures in Ukraine.

EU chief Ursula von der Leyen meanwhile arrived in Kyiv to mark the Europe Day celebration of peace and unity, a symbolic retort to Moscow's Victory Day military parade.

During his brief address, Putin also told the columns of Russian military personnel in ceremonial uniform in central Moscow that the country's future rests on Russian soldiers fighting in Ukraine.

"Today civilisation is again at a decisive turning point," Putin said standing shoulder to shoulder with elderly veterans and soldiers from Russia's Ukraine campaign.

"A war has been unleashed against our motherland," he said, adding that "the future of our statehood and our people depend on you."

"For Russia, for our armed forces, for victory! Hurrah!"

Yet the celebrations to mark the anniversary of the Soviet Union's victory over Nazi Germany 78 years ago have been overshadowed by the military's slow gains and heavy losses in Ukraine.

- Wagner accusations -

In remarks released at the same time as Putin's speech, the head of the Wagner outfit accused some Russian forces of abandoning their positions near Bakhmut, the epicentre of the fighting in Ukraine.

"They all fled, exposing the front," Prigozhin said, repeating a vow that his men would leave Bakhmut by May 9 if the Russian military does not supply more ammunition.

Wagner has been leading Russia's months-long assault for Bakhmut, a destroyed industrial town in eastern Ukraine, where Russian forces have little to show after a winter offensive.

"Why is the state not able to defend its country?" Prigozhin said in a scathing video, in which he also accused Russian military top brass of trying to "deceive" Putin on how the Ukraine campaign was being led.

Putin, increasingly isolated on the world stage since launching the conflict last February, was nonetheless surrounded on Red Square by leaders of several ex-Soviet states, including Armenia and Kazakhstan.

In the run-up to Victory Day, Russia was hit with several acts of sabotage, including an explosion that derailed a train, a drone attack on the Kremlin and a car bomb that wounded a pro-Kremlin writer.

Kremlin spokesman Dmitry Peskov said that "all necessary measures" were being taken to ensure the safety of the leaders.

Still more than two dozen cities and towns cancelled plans to stage their own military parades over security concerns.

Since coming to power in 2000, Putin has stoked patriotic fervour around the 1945 Soviet victory over the Nazis, boosting his standing as the heir of Soviet power.

The Kremlin has also used the memory of the Soviet war effort to justify its offensive in Ukraine, claiming it is fighting "fascists" supported by the West.

- 'European family' -

The president of the European Commission meanwhile travelled by train from Poland to Kyiv to meet with Ukrainian President Volodymyr Zelensky and work on his country's quest for eventual EU membership.

Zelensky has decreed that May 9 would be celebrated in his country as Europe Day, as it is in Brussels, spurning the martial Victory Day tradition of the former Soviet Union.

"I very much welcome President Zelensky's decision to make May 9 the Day of Europe. Ukraine is part of our European family," von der Leyen told a reporter on her train to Kyiv.

"My presence in Kyiv today on May 9 is symbolic, but it is also the sign of a crucial and very  practical reality: the EU is working hand in hand with Ukraine on many issues."

Shortly before she arrived, Ukraine's air force said it had downed 23 out of 25 cruise missiles launched by Russia in the night between Monday and Tuesday.

The air alert in Kyiv ended about an hour before von der Leyen's arrival.