Official results of the weeklong vote that ended July 1 showed that 77.92 percent of Russian voters endorsed the constitutional changes, with only 21.26 against. Turnout was 68 percent, the Central Election Commission said.

"Such a high turnout and such a high level of support was very difficult to predict," Peskov said in a statement to reporters.

Other officials quickly chimed in.

"A plebiscite on trust in Putin ended with victory for the head of state," State Duma speaker Vyacheslav Volodin was quoted as saying in the lower house of parliament's official newspaper. Moscow Mayor Sergei Sobyanin lauded "a plebiscite on the consolidation of society around the Russian president."

Kremlin critics were struck by the retroactive portrayal of the vote as a plebiscite on support for Putin. His name was almost completely absent from promotional material and TV reports urging Russians to vote on a package of over 200 constitutional amendments -- despite the fact that a clause allowing Putin to reset term limits was among the most consequential of them.

They also alleged that the high turnout and support reflected in official results were engineered to conform with targets set down well in advance by Putin's aides.

"The updated 'results' are fake and a huge lie," said opposition politician Aleksei Navalny, who had called on his supporters to boycott the vote. "They have nothing in common with the opinion of Russia's citizens."

Claims of fraud quickly began mounting.

The most damning came from Sergei Shpilkin, a prominent electoral researcher who uses data from Russia's Central Election Commission during voting cycles to plot tallies reported at polling stations throughout the country and detect evidence of inflated turnout.

During the presidential election of 2018, which Putin won handily, Shpilkin saw that the data showed numerous polling stations reporting turnout percentages ending in 0 or 5, suggesting, per his widely cited analysis, that almost 10 million votes were falsified at the ballot box.

This time, Shpilkin said, that figure was an "unprecedented" 22.4 million.

Adding to the murky picture, exit polls conducted by anti-government activists in Moscow and St. Petersburg showed that a small majority in the two cities -- both strongholds of the embattled opposition -- had voted against the proposed changes. But the activists could only record the views of voters who agreed to be interviewed, meaning they had few means of gauging the actual scale of ballot manipulation.

The plebiscite was marred by inconsistencies from the start, not least because few official rules governed its execution. From the first day of voting, Russians could cast ballots in car trunks, parked buses and on tree stumps, as evidenced by various images posted to social media from across the country.

By the afternoon of July 1, the election commission was already reporting preliminary results, apparently in violation of laws that usually apply to national votes.

A Russian woman living in Israel reported that she'd been able to vote three times -- in Tel Aviv, in Haifa, and again online. At one Moscow polling station, a man was told that he and two of his children had already cast their votes -- despite insisting none of them had. A supervisor then seized the voter record, snapped it shut, and told the man, "Prove it!"

Daily raffles offered prizes to all who cast their ballot. Posters with "YES" written across them hung in the basements of apartment blocks in major cities. And at least one journalist who tried to document events inside a polling station was violently apprehended by police.

There was also plenty of evidence suggesting the vote had been a mere formality. At least two weeks before voting even began, bookshops across Moscow were selling copies of the Russian Constitution with the new amendments included.

In a statement on July 2, the day after voting ended, election monitor Golos issued a scathing assessment of the vote, saying that much of the balloting had been falsified -- and results partly determined in advance.

"The actual voting process had no significant meaning," the organization said. "An expression of the people's will was impossible from the start, because of the rules that were consciously put in place by the organizers."

Calling the vote "unprecedented" in terms of the scale of fraud and manipulation, the organization concluded that it will "go down in the country's history as an attack on the people's sovereignty."