Vladimir Putin said Russia would not be "intimidated" as he hailed an election victory that paves the way for the former spy to become the longest-serving Russian leader in more than 200 years.

All of the 71-year-old's major opponents are dead, in prison or exiled, and he has overseen an unrelenting crackdown on anybody who publicly opposes his rule or his military offensive in Ukraine.

"I want to thank all of you and all citizens of the country for your support and this trust," Putin told a news conference at his campaign headquarters in Moscow early Monday, hours after polls closed.

"No matter who or how much they want to intimidate us, no matter who or how much they want to suppress us, our will, our consciousness - no one has ever succeeded in anything like this in history. It has not worked now and will not work in the future. Never," he added.

With more than 99 per cent of voting stations having submitted results, Putin had secured 87 per cent of all votes cast, official election data showed, according to state news agency RIA.

It is a record victory in a presidential election where he faced no genuine competition.

The three-day election was marked by a surge in deadly Ukrainian bombardments, incursions into Russian territory by pro-Kyiv sabotage groups and vandalism at polling stations.

The Kremlin had cast the election as a moment for Russians to throw their weight behind the full-scale military operation in Ukraine, where voting was also being staged in Russian-controlled territories.

'Drunk from power'

Putin singled out Russian troops fighting in Ukraine for special thanks in his post-election speech in Moscow.

And he was unrelenting in claiming his forces had a major advantage on the battlefield, even after a week that saw Ukraine mount some of its most significant aerial attacks on Russia and in which pro-Ukrainian militias launched armed raids on Russian border villages.

"The initiative belongs entirely to the Russian armed forces. In some areas, our guys are just mowing them - the enemy - down," he said.

Kyiv and its allies slammed the vote as a sham. President Volodymyr Zelensky lashed out at Putin as a "dictator" who was "drunk from power".

"There is no evil he will not commit to prolong his personal power," Zelensky said.

As early as Friday, the first day of voting, EU chief Charles Michel had sarcastically congratulated Putin on his "landslide victory".

Britain's foreign minister David Cameron added his voice to the protests, saying "this is not what free and fair elections look like", while the United States criticised the holding of the vote in Ukrainian territories occupied by Moscow.

The leaders of Venezuela, Nicaragua, Cuba and Bolivia congratulated Putin on his re-election.

If he completes another full Kremlin term, Putin will have stayed in power longer than any Russian leader since Catherine the Great in the 18th century.

Allies of the late Alexei Navalny - Putin's most prominent rival, who died in an Arctic prison last month - had tried to spoil his inevitable victory, urging voters to flood polling stations at noon and spoil their ballots.

His wife, Yulia Navalnaya, was greeted by supporters with flowers and applause in Berlin. After voting at the Russian embassy, she said she had written her late husband's name on her ballot.

A defaced election ballot paper with the hand-written inscription 'Navalny Alexei Anatolyevich, 1976, the man who was giving me the hope' is seen left at the grave of late Opposition leader Alexei Navalny on the day of presidential elections. Photo: AFP

'Mr Navalny'

Some voters in Moscow answered the opposition's call, telling AFP they had come to honour Navalny's memory and show their defiance in the only legal way possible.

"I came to show that there are many of us, that we exist, that we are not some insignificant minority," said 19-year-old student Artem Minasyan at a polling station in central Moscow.

Putin said the protest had had no impact and that those who spoiled their ballots would "have to be dealt with".

In his first public comments on Navalny's death last month, Putin called his passing a "sad event".

Using his name in public for the first time in years during a televised news conference, Putin said: "As for Mr. Navalny. Yes, he passed away. This is always a sad event."

Putin said a colleague had proposed swapping Navalny several days before he died for "some people" currently held in prisons in Western countries.

"The person who was talking to me hadn't finished his sentence and I said 'I agree'".

Former Russian leader Dmitry Medvedev also congratulated Putin on his "splendid victory" long before the final results were due to be announced.

And state-run television praised how Russians had rallied with "colossal support for the president" as well as the "unbelievable consolidation" of the country behind its leader.

'Not alone'

At Navalny's grave in a Moscow cemetery, AFP reporters saw spoiled ballot papers with the opposition leader's name scrawled across them on a pile of flowers.

"We live in a country where we will go to jail if we speak our mind. So when I come to moments like this and see a lot of people, I realise that we are not alone," said 33-year-old Regina.

There were repeated acts of protest in the first days of polling, with a spate of arrests of Russians accused of pouring dye into ballot boxes or arson attacks.

Any public dissent in Russia has been harshly punished since the start of Moscow's offensive in Ukraine on February 24, 2022 and there were multiple warnings from the authorities against election protests.

The OVD-Info police monitoring group announced that at least 80 people had been detained across nearly 20 cities in Russia for protest actions linked to the elections.