Vladimir Putin has praised the Soviet role in defeating fascism, as Russia marked the anniversary of the second world war victory over Nazi Germany.

In a speech to soldiers and war veterans gathered on Moscow's Red Square for the annual Victory Day military parade, Putin said those who defeated fascism must never be betrayed.

The message had a poignant ring because Moscow has warned of the dangers posed by leaders it portrays as neo-fascists in Ukraine, and urged Europe to prevent the rise of the far-right.

Troops in armoured personnel carriers salute during the Victory Day parade. Photograph: Grigory Dukor/Reuters

"The iron will of the Soviet people, their fearlessness and stamina saved Europe from slavery. It was our country which chased the Nazis to their lair, achieved their full and final destruction, won at the cost of millions of victims and terrible hardships," the Russian president said.

"We will always guard this shining and unfading truth and will not allow the betrayal and obliteration of heroes, of all who, not caring about themselves, preserved peace on the planet."

Victory Day parades are also being held in Crimea and parts of east Ukraine held by pro-Moscow militia. The Russian deputy prime minister, Dmitry Rogozin, was at a parade in the breakaway Trans-Dniester region of Moldova, where Russia has stationed troops since 1990. He told a crowd of 2,000 "the plague of fascism is thriving" and referred specifically to the deaths of mainly pro-Russians in Odessa, Ukraine, last week. Further violence was reported on Friday in the Ukrainian port city of Mariupol. A Ukrainian news website, Insider, said eight pro-Russians had been killed.

Russia annexed Crimea from Ukraine in March after a pro-European government took power in Kiev following the ousting of Viktor Yanukovich as president. There is international concern that Russia could seize parts of eastern Ukraine, where pro-Russia separatists have taken control of several towns and key buildings in the city of Donetsk. The leadership in Kiev dismisses charges that neo-fascism is on the rise.

Pro-Russian separatists occupying public buildings in eastern Ukraine have pledged to press ahead with a referendum on Sunday to establish their own "republic" despite Russia calling for the vote to be postponed.

"The referendum will happen on May 11," the leader of the separatists' self-styled Donetsk People's Republic, Denis Pushilin, said on Thursday. "The date of the referendum will not be postponed."

A separate secessionist referendum has been called for the neighbouring eastern region of Luhansk.

The EU has denounced the plebiscite plans, while Nato has said there was no evidence to support Vladimir Putin's announcement that up to 40,000 Russian troops had been withdrawn from Ukraine's eastern border.

The eastern rebel-held town of Slavyansk was in a state of confusion following Russia's apparent U-turn on the referendum. Putin had previously offered his tacit support to the Donetsk separatists and repeatedly pledged to intervene to protect Russian speakers in Ukraine's east if they come under threat.

The rebel leaders were adamant on Thursday that the referendum would go ahead.

"If we don't have a referendum on the 11th then we will lose the trust of the people," a spokesperson said. "We face the choice: referendum or war, and we choose the peaceful way."

It remains unclear how the voting will take place since the rebels control only pockets of the regions. Militia fighters in Slavyansk, where gunfights with the Ukrainian army have become an almost nightly occurrence, reacted angrily to the news of Russia's postponement request. "He [Putin] is a coward," said Ruslan, a militia guard standing in front of the city's rebel headquarters.

About a dozen rebel fighters are thought to have died in clashes with the Ukrainian army over the last week in Slavyansk, as well as three civilians caught in crossfire.