An organization of Russian activist groups is dismissing the results of Sunday's presidential election, calling Vladimir Putin's win an “insult” to the Russian people.

The League of Voters issued a statement at a news conference Wednesday, alleging its monitors found evidence of widespread violations and vote-rigging. The activist group is calling for a new, mass rally Saturday but is concerned the public's resolve may be fading.

Writer and league member Boris Akunin told reporters he expected a “certain public stagnation” and lower turnout for Saturday's rally. He said many people are likely feeling “numb” after Mr. Putin's win.

Russia's election commission says Mr. Putin received almost 64 percent of the vote in winning a six-year term as president. Election officials have rejected allegations of voting irregularities. Mr. Putin's spokesman, Dmitry Peskov, also dismissed the allegations Wednesday, saying the “matter is closed.”

Mr. Putin, who has been prime minister since relinquishing the presidency in 2008, called the election an “open and honest struggle.” International observers say the election was clearly skewed in Mr. Putin's favor. They also reported voting irregularities at one-third of the polling stations.

On Tuesday, prominent Russian activist Alexei Navalny promised a campaign of civil disobedience, accusing Mr. Putin of stealing the presidential election. He said tens of thousands of people will turn out for street protests in Russian cities and will keep up the protests until their demands are met.

Police arrested Navalny and hundreds of other opposition supporters at an anti-Putin rally in Moscow Monday. They were later released. Many of the protesters chanted “Russia without Putin” and “Power to millions, not to the police.”

World leaders acknowledged Mr. Putin's victory with reservations. European Union foreign affairs chief Catherine Ashton urged Russian leaders to address the “shortcomings” identified by international observers.

The U.S. State Department congratulated the Russian people on the completion of the presidential poll and said it looks forward to working with the president-elect. But it also urged Moscow to launch an “independent and credible” investigation of all reported electoral violations.