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MOSCOW — The United States harshly criticized Russia's detention of opposition leader Alexei Navalny and hundreds of other protesters Sunday in central Moscow.

A Reuters reporter saw police detain Navalny, who called the rally to protest corruption, on Moscow's Tverskaya Street and put him in a police truck. Hundreds of opposition protesters crowded around the police van and tried to prevent it from taking him away.

A tweet from Navalny's account after the incident said: "Guys, I'm all right. Don't try to break me out. Go on walking down the Tverskaya. Our topic today is fight against corruption."

The United States said it was monitoring developments and called on Russia to release all of the protesters. Mark Toner, acting spokesman for the U.S. State Department, called the arrests "an affront to core democratic values."

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"The Russian people, like people everywhere, deserve a government that supports an open marketplace of ideas, transparent and accountable governance, equal treatment under the law and the ability to exercise their rights without fear of retribution," Toner said.

The arrests came as Russian protesters denouncing corruption gathered across Russia, and some scuffled with police.

Photos: Hundreds Detained in Moscow Protest of Government Corruption

The protest appears to be one of the largest coordinated outpourings of dissatisfaction since the 2011-12 demonstrations following a fraud-tainted parliamentary election.

The demonstrations, driven by Navalny, focus on his recent claims that Prime Minister Dmitry Medvedev has amassed a collection of mansions, yachts and vineyards.

Moscow police told the TASS news agency that the number of people detained was "more than 500." Police said those detained will face "administrative prosecution," or fines and arrests.

But the final tally of those detained in Moscow was 700, according to the human rights monitoring group OVD-Info.

Image: Police detain a demonstrator at a rally Sunday in central Moscow. Maxim Shipenkov / EPA

Navalny's press secretary, Kira Yarmush, said on Twitter that people at his office had been detained and that Leonid Volkov, the head of the office and co-founder of Navalny's unregistered Party of Progress, was facing extremism charges.

Some demonstrators have showed up with their faces painted green, a reference to a recent attack on Navalny when an assailant threw a green antiseptic liquid onto his face.

It isn't the first time Navalny has been in trouble with the police. Just last month, he was convicted of embezzling 16 million rubles ($270,000) in 2009.

At the time, Navalny said the conviction was an effort to stop him from challenging President Vladimir Putin's party in coming elections. People with criminal convictions are ineligible to run for office in Russia.