Witnesses said Garry Kasparov, the former world chess champion who has emerged as the most prominent leader of the opposition alliance, was seized as he tried to lead a small group of demonstrators through lines of police ringing Pushkin Square. He was freed late Saturday after he was fined $38 for participating in the rally.
A coalition of opposition groups organized the "Dissenters March" to protest the economic and social policies of President Vladimir Putin as well as a series of Kremlin actions that critics say has stripped Russians of many political rights.
About 1,000 protesters took part in the rally, chanting slogans such as "Russia without Putin," "For free and fair elections," and "For a different Russia," reports CBS News correspondent Svetlana Berdnikova. The protesters were holding flags of the Red Youth Vanguard, the banned National Bolshevik Party, and the United Civic Front.
According to the official sources at the internal ministry, there were about 9000 police officers massed to keep the demonstrators off Pushkin Square, reports Berdnikova beating some protesters and detaining many others.
Police said 170 people had been detained but a Kasparov aide, Marina Litvinovich, said as many as 600 people were detained — although she said about half were released quickly.
"It is no longer a country ... where the government tries to pretend it is playing by the letter and spirit of the law," Kasparov said outside the court building, appearing unfazed by his detention.
"We now stand somewhere between Belarus and Zimbabwe," two dictatorships that have cracked down on opposition, he said.
It was the fourth time in recent months that anti-Putin demonstrations — all called Dissenters Marches — have been broken up with force or smothered by a huge police presence. Earlier protests were thwarted in Moscow, St. Petersburg and Nizhny Novgorod.
A similar march planned for Sunday in St. Petersburg also was banned by authorities.
This weekend's marches were being closely watched as a barometer of how much of a threat, if any, opposition forces pose to the Kremlin as Russia prepares to hold parliamentary elections in December and a presidential vote next spring.
Putin, whose second and last term ends in 2008, has created an obedient parliament and his government has reasserted control over major television networks, giving little air time to critics.
TV newscasts on Saturday reported the protests, but gave as much or more time to a pro-Kremlin youth rally held near Moscow State University.
Later, police charged into a crowd of about 200 demonstrators outside the police precinct where Kasparov was being held, beating protesters with nightsticks and fists.
Kasparov and his allies mustered, by their own reckoning, about 2,000 people — far fewer than the 30,000 people who patronize the McDonald's restaurant at Pushkin Square on an average day.
But some protesters said they were not discouraged by the small turnout or intimidated by the overwhelming force marshaled to block the rally.
Andrei Illarionov, a former Putin economics adviser who has become a Kremlin critic, pointed out that in 1968 only six people appeared in Red Square to protest the Soviet invasion of Czechoslovakia.
"This is a crime against the Russian constitution," he said. "This country is not free anymore and the main criminal in Russia right now is the authorities."
About 100 of those detained at Pushkin Square belong to the ultranationalist National Bolshevik Party, party spokesman Alexander Averi said. But he said Eduard Limonov, the novelist who heads the party known for street theater and political pranks aimed at Putin, evaded a detention attempt.
The demonstration's organizers sought permission to gather on Pushkin Square, a traditional site for protests, but city officials rejected the request. Instead, they approved the use of Turgenev Square, about a mile to the east and away from the city's commercial and cultural hub.
Organizers refused to cancel plans for the Pushkin Square rally and protesters started to arrive before 11 a.m. Police began seizing them a few at a time.
A 23-year-old woman, who gave her name only as Maria, said she and her husband, Andrei, were coming out of the subway when officers grabbed him.
"We didn't do anything," she said, tears rolling down her face as she watched her husband being hustled into a police truck. "We just wanted to see what would happen."
Viktor Vinokourov, a 67-year-old pensioner, watched the detentions from a nearby sidewalk, holding a hand-scrawled sign declaring: "I Don't Agree." A young man in a leather coat, apparently a plainclothes security officer, snatched it out of his hands.
Around noon, several hundred protesters headed away from Pushkin Square toward the sanctioned demonstration site, marching past startled motorists while chanting "Putin get out!" and "We need a new Russia!"
As they walked arm-in-arm down a main thoroughfare, a police cordon blocked their path. Some in the crowd ran forward and police charged, their truncheons flailing.
A Japanese journalist suffered a gash on the head and was treated by a policeman in a riot helmet. Eventually the crowd of protesters melted into side streets, and many joined about 1,000 demonstrators at the authorized site.
Hundreds of police and soldiers surrounded the square, but let demonstrators in after checking them for weapons.
In a speech there, Mikhail Kasyanov, Putin's first prime minister but now a leading opponent, denounced the arrests and beatings.
"Everyone should ask the question: What is happening with our authorities — are they still sane, or have they gone mad?" he said, as the crowd chanted "Shame on the government."
Moscow Mayor Yuri Luzhkov, who observed the march, said authorities were seeking only to maintain order, not to interfere with the exercising of political rights.
"We live in a democratic country, a free country, and we give the possibility to everybody to express their agreement or disagreement," he said, in remarks carried on Russia's Channel 1 television.