Russian President Vladimir Putin justified the invasion of Ukraine at a rally in Moscow on Friday, where his speech was abruptly cut off on the state TV broadcast in what the Kremlin described as a technical error.

Tens of thousands of people waved the Russian flag at the national stadium. They took part in celebrations commemorating the eighth year of Russia's annexation of Crimea, which is deemed illegal by the Ukrainian government and not recognised in the West.

Speaking from a stage in front of a banner that read, "For a world without Nazism," Putin said Russia "will definitely implement all our plans" in Ukraine.

"To spare people from this suffering, from this genocide, this is the main reason, motive and purpose of the military operation that we launched in the Donbas [an eastern Ukrainian region] and Ukraine," he said.

Russian state TV later replayed Putin's full speech without problems, but the Kremlin refused to confirm or deny if the event was live or pre-recorded.

Russian President Vladimir Putin justified the invasion of Ukraine at a rally in Moscow on Friday, where his speech was abruptly cut off on the state TV broadcast in what the Kremlin described as a technical error.

Tens of thousands of people waved the Russian flag at the national stadium. They took part in celebrations commemorating the eighth year of Russia's annexation of Crimea, deemed illegal by the Ukrainian government and not recognized in the West.

Speaking from a stage in front of a banner that read, "For a world without Nazism," Putin said Russia "will definitely implement all our plans" in Ukraine.

"To spare people from this suffering, from this genocide -- this is the main reason, motive and purpose of the military operation that we launched in the Donbas [an eastern Ukrainian region] and Ukraine," he said.

Russian state TV later replayed Putin's full speech without problems, but the Kremlin refused to confirm or deny if the event was live or pre-recorded.

Putin insisted that national unity was the strongest in a long time, even as many people flee Russia or protest against war in the streets, and as the country is increasingly isolated on the global stage. US and Western intelligence officials have also observed that Russia is having difficulty replacing its forces, which is having a significant impact on troop morale, senior NATO officials said on Wednesday.

"It becomes more evident every day that Putin gravely miscalculated," a senior NATO intelligence official told reporters at the alliance's headquarters on Wednesday night, speaking on the condition of anonymity to disclose sensitive assessments. "Russia continues to face difficulties replacing its combat losses, and increasingly seeks to leverage irregular forces, including Russian private military corporations and Syrian fighters."

But none of that pessimism was evident in Putin's speech on Friday. "It so happened that the beginning of the operation ... quite by chance coincided with the birthday of one of our outstanding military leaders [and] canonized saints, Fyodor Ushakov, who in his entire brilliant military career did not lose a single battle," he told the crowd.

"He once said that these thunderstorms will go to the glory of Russia. So it was then, so it is today, and so it will always be!"