Thousands of people across Russia protested corruption on Sunday, leading to scores of arrests, including that of opposition leader Alexei Navalny.

An anti-corruption campaigner who plans to challenge President Vladimir Putin in next year's presidential elections, Navalny was detained by police as he walked along central Moscow's Tverskaya Street with supporters. State news agency Tass cited Moscow police as saying there were at least 500 other arrests.

The protests have been judged the largest in six years and come a year before Putin's attempt to win a fourth term in office. Shortly before he was arrested, Navalny said, "I'm happy that so many people came out (onto the streets) from the east (of the country) to Moscow."

The White House issued a statement condemning the mass arrests, saying the arrests represented "an affront to core democratic values." 

Navalny and the Foundation for Fighting Corruption had called for protests in dozens of cities, from Vladivostok in the Far East to Moscow. Most of the planned protests in 99 cities were banned by authorities, but thousands showed up at rallies anyway.

In Moscow, police estimated there were about 8,000 protesters. In St. Petersburg, about 4,000 people showed up in the city center.

Medvedev accused

Navalny published a report earlier this month accusing Prime Minister Dmitry Medvedev of owning mansions, yachts and vineyards through a shadowy network of nonprofit organizations supported by oligarchs.

A YouTube video Navalny posted outlining the allegations has been viewed 11 million times.

The Russian government shrugged off the allegations, suggesting it was election propaganda.

Navalny says he still plans to run against Putin in next year's presidential elections despite legal troubles that may block his name from the ballot.

A recent court decision upheld a fraud conviction and a five-year suspended sentence that critics say is politically motivated.

ls,cw/jm