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Tens of thousands of people marched in downtown Moscow for three hours Saturday to protest against alleged electoral fraud by Russian Prime Minister Vladimir Putin in last weekend's parliamentary elections -- and to call for Putin to step down.

The government-sanctioned demonstrations in 60 cities across the country marked the largest display of public discontent in post-Soviet Russia. Chants of "Russia without Putin!" were the loudest heard at the Moscow protest.

Police estimated that about 30,000 people gathered in Moscow's main square and surrounding side streets to denounce the election results. However, organizers estimated that anywhere from 40,000 to 100,000 demonstrators were on hand for the rally.

CNN Moscow reporter Phil Black told Â鶹´«Ã½ Channel the demonstration in Bolotnaya Square was "an unprecedented event -- very peaceful but loud and passionate."

He said the key message the demonstrators were trying to send to the Kremlin was that "this is not a revolution" but simply a protest against the questionable results of last Sunday's parliamentary elections, in which Putin's United Party narrowly retained a majority of seats.

"The belief is that if the election had been fair, then the losses would have been even steeper," Black said. He pointed out that protesters believe that the United Party should only have had 25 per cent of the vote, not the 50 per cent that was recorded.

"These people very strongly believe that if not for unfairness in the election system and in the way that vote was conducted that Vladimir Putin and his party would not be holding onto power."

Even though the government had allowed the protests, provided they had permits and were peaceful, Black said, "The government here is not looking to bow to this pressure at all."

Still, the protest will go on, he said, adding: "The organizers see this as a first step in a longer campaign."

State-controlled TV channels that usually ignore or deride the opposition gave notable airtime to the protests. A top United Russia official, Andrei Isayev, acknowledged late Saturday that "expression of this point of view is extremely important and will be heard in the mass media, society and the state."

Reports of vote-rigging have acted as a catalyst for long-simmering discontent of many Russians just three months before Putin is to seek a third term as president. He previously served as president from 2000 to 2008.

Golos, Russia's independent elections observer, reported Saturday that Putin's United Russia party "achieved the majority mandate by falsification," citing widespread voting irregularities.

"The falsifications that authorities are doing today have turned the country into a big theatre, with clowns like in a circus," said Alexander Trofimov as he joined the protest in the square adjacent to the Kremlin.

"I'm not very involved in politics but I was indignant with the election outcome. Many of my friends were involved in the election as monitors and witnessed great violations. We don't like the feeling of being cheated," said Daria Sviridova, a 35-year-old psychologist who came to the rally clutching white flowers, a symbol of the movement's call for "clean" elections.

"I don't think any citizen of the country can say he is very happy with anything. We don't have an independent judiciary, there is no freedom of expression -- all this combined creates a situation where people are forced to protest," said demonstrator Albert Yusupov, a Russian soldier who was dressed in civilian clothes.

"Every person who thinks of themselves as a citizen has a right to go and protest," said Boris Alexandrov, a 20-year-old computer science student at Moscow State University. He paused to join a chant of "Those were not elections!" before continuing. "But none of the parties represent my point of view. Not one."

Late Saturday, Putin's press secretary, Dmitry Peskov, issued a statement in which he acknowledged that protesters were "displeased" with the elections.

"We respect the point of view of the protestors, we are hearing what is being said, and we will continue to listen to them," the statement said. "The citizens of Russia have a right to express their point of view, in protest and in support, and those rights will continue to be secured as long as all sides do so in a lawful and peaceful manner."

In the Pacific city of Vladivostok, several hundred protesters rallied along a waterside avenue where some of Russia's Pacific Fleet warships are docked. They shouted "Putin's a louse" and some held a banner caricaturing United Russia's emblem, reading "The rats must go."

Police reported making about 100 arrests across the country. The Interfax news agency reported the arrest of about 15 protesters in the Siberian city of Perm and about 30 in the Far Eastern city of Khabarovsk.

Russian President Dmitry Medvedev conceded this week that election law may have been violated and Putin has suggested "dialogue with the opposition-minded."

When U.S. Secretary of State Hillary Clinton called the vote unfair on Friday and urged an investigation into fraud, Putin reacted by accusing Clinton and the United States of instigating the street protests and trying to undermine Russia.

With files from The Associated Press