MOSCOW — President Vladimir Putin's United Russia party maintained its tight grip on the nation's parliament in three-day elections criticized by opposition parties and independent observers for ballot stuffing and tampering, according to election results announced by the Central Election Commission.

Central Election Commission (CEC) head Ella Pamfilova said United Russia won, holding on to its supermajority in the parliament. The turnout, at 51.68 percent, surpassed the 2016 turnout of 47.88 percent, which was the lowest in Russian history.

Opposition leaders attacked an opaque online voting system used in six regions, including Moscow, claiming it was manipulated to fraudulently overturn opposition wins in some seats and deliver them to United Russia.

Jailed opposition leader Alexei Navalny said “the slick hands of the United Russia falsified the results” in seats won by opposition candidates endorsed by his Smart Voting initiative — a system to direct voters to the candidates most likely to defeat Putin’s party.

The Communist Party, which came in second as usual, refused to recognize the online results.

Police cordoned off Pushkin Square in central Moscow after Communist Party chief Gennady Zyuganov called for protests to “defend the election as the cadets of Podolsk defended Moscow,” a reference to a group of military students who resisted Nazi invaders approaching Moscow in 1941 during the Great Patriotic War (as World War II is known in Russia).

Moscow Mayor Sergei Sobyanin denied Communist Party applications to stage protests Monday, Tuesday or Friday, citing coronavirus pandemic restrictions. Russian authorities have often used restrictions to curb opposition figures, even as they have allowed other rallies and mass events, some of which Putin has attended.

Putin’s party has won all five State Duma elections since 2003 — three of them with a supermajority — giving the Kremlin a compliant parliament that has long supported the Russian president as he cracked down on political freedoms and crushed his opponents.

A supermajority, or two-thirds of the 450 seats, allows United Russia to change the constitution without opposition support, dominate committees and ram through laws with little debate.

United Russia’s approval rating was hovering around 30 percent in the months leading to elections, according to independent pollster the Levada Center, because of voter discontent over increases in the pension age, high food prices, declining real wages and the handling of the coronavirus pandemic.

Kremlin spokesman Dmitry Peskov said the election was “competitive, open and fair.”

“The competitiveness, openness and fairness of the past elections certainly mattered and matters above all for the president, and we definitely view the past electoral process very, very positively in this respect,” Peskov said Monday.

A U.S. State Department statement said the conditions surrounding the election were “not conducive to free and fair proceedings.” It criticized both the “widespread efforts to marginalize independent political figures” before the vote and use of laws to restricting people’s political rights.

“We call upon Russia to honor its international obligations to respect human rights and fundamental freedoms and to end its pressure campaign on civil society, the political opposition, and independent media,” the statement said.

“But we have number of reports from independent local observers that were reporting a lot of irregularities during these elections.”

Political analyst Tatiana Stanovaya, founder of independent R. Politik political consultancy, said Russia’s parliament vote was not really an election but “the administering of a planned result.” Eight parties, including Kremlin-friendly factions and several independents, were expected to get seats.

“As expected, the system’s knee-jerk reaction was to maximise the result, while the level of control over the situation was very high,” she wrote in a post on social media. “The problem with this result is not only that the public won’t believe it (the kind of legitimacy the Kremlin absolutely doesn’t think it needs) but the elites won’t either.”

She said anger in the Communist Party over the result could push it to become a genuine opposition force instead of a compliant parliamentary faction those poses no real threat.

The United Russia supermajority will enable the Kremlin to maintain its tight political control over the country. Delivering a United Russia victory was seen as particularly important, with presidential elections due in 2024, in which Putin is expected to seek his fifth term in office after constitutional term limits were ditched in another controversial vote last year. Putin last year gained the right to contest two more terms, meaning he could rule until 2036.

The three-day elections took place against the background of a sweeping crackdown on the opposition, human rights activists and independent journalists.

Opposition leader Alexei Navalny is in jail. His electoral network was declared an extremist organization in June and effectively banned. Its leaders, other opposition figures, human rights activists, human rights lawyers and independent journalists have been arrested or fled the country. Dozens of opposition candidates were barred from running or withdrew.

With voting over three days, independent observers and opposition figures complained that in many cases ballots were not properly secured at night. Russian social media was flooded with videos of blatant ballot stuffing and thugs intimidating observers and independent journalists.

Opposition candidates complained of cases where observers were denied access to polling stations by officials or were pushed away by unidentified thugs or arrested by police.

But elections chief Pamfilova said there were fewer violations than in previous elections.

“In terms of transparency, our system is one of the most transparent in the world,” Pamfilova told Putin in a phone call to report on the election.

Aside from ballot stuffing and the barring of opposition candidates, the main controversy has been the opacity of the online voting used in six regions and long delays in the release of these results — a system likely to go national in the next presidential election. Analysts warn that there is no way to verify election results with the online approach.

Final results will be released Friday. Nikolai Bulayev, deputy head of the CEC, said there were no problems with the uploading of online votes.

“All of the uploaded data correctly represents the voting results,” Bulayev said. Artem Kostyrko, a Moscow official, said the long delays in publishing online results is due to the large number of votes.

A number of opposition candidates, including those from the Communist Party, were well ahead of United Russia in paper balloting but fell behind dramatically when online votes were announced Monday. Opposition figures claimed authorities used online votes to overturn opposition wins seen in the verifiable paper balloting.

Valery Rashkin, head of the Moscow branch of the Communist Party, said there were clear violations in online voting with candidates winning in paper ballots but scoring an inexplicably low vote in online voting.

“It is the same all over Moscow,” he said. “It is a total violation.” He called on voters to reject the stolen election and “come out with us to fight for your rights.”

Liberal Democratic Party (LDP) leader Vladimir Zhirinovsky said the government party had won for 20 years and the country was heading toward a Belarusian situation, referring to last year’s mass protests over President Alexander Lukashenko’s victory claim in elections rejected by the opposition.

“I want to vomit,” he said.

“It’s total stupidity. What a country! The situation has worsened everywhere,” he said at a news conference, “ and they are partying,” referring to United Russia’s victory parties.

“We are making great strides toward a Belarus scenario, and they don’t understand. They’re blind.”

In southwest Moscow, Mikhail Lobanov, a university lecturer and urban activist, who is not a communist but ran as a Communist Party candidate, was endorsed by Navalny’s Smart Voting and was ahead after the counting of paper ballots against a high profile United Russia candidate, state TV anchor Yevgeny Popov.

Lobanov said Monday he had been winning with a margin of more than 10,000 votes. But when online votes landed Monday, Popov had a lead of more than 20,000 votes. Lobanov called the online results “insane.”

“The result is not surprising, but it is outrageous,” he said. “Such a gigantic difference in the results of voting in precincts on the ground and online voting results cannot be true.

“We can determine the accuracy of counting at the polls because it involves independent observers. But electronic voting is just a black box that was deliberately hidden from us for more than 12 hours.”