Mr Navalny, an anti-corruption campaigner who is leading the opposition to President Vladimir Putin, was arrested while walking from a nearby subway station to the demonstration in Pushkin Square.

Mr Navalny and his Foundation For Fighting Corruption had called for the protests, which attracted crowds of hundreds or thousands in most sizeable Russian cities, from the Far East port of Vladivostok to the European heartland.

The protests appeared to be one of the largest coordinated outpourings of dissatisfaction in Russia since the massive 2011-12 demonstrations that followed a fraud-tainted parliamentary election.

The protests on Sunday focused on reports by Mr Navalny's group claiming that Prime Minister Dmitry Medvedev has amassed a collection of mansions, yachts and vineyards.

The alleged luxuries include a house for raising ducks, so many placards in Sunday's protests showed mocking images of yellow duck toys.

In the Pacific coast city of Vladivostok, police forcefully detained some demonstrators near the city's railway terminal, in one case falling down a small grassy slope as they wrestled with a detainee.

News reports and social media reported demonstrations in large cities throughout the country including Novosibirsk, Tomsk and Krasnoyarsk. At least 25 people were reported arrested in Vladivostok and 12 in Khabarovsk.

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

There were no immediate figures on the demonstration size in Moscow but the one-hectare Pushkin Square was densely crowded as were pavements on the adjacent Tverskaya Street, suggesting that more than 10,000 people had showed up.

Scuffles with police erupted sporadically and some demonstrators were arrested, including a grey-haired man who police dragged along the pavement.

"It's scary, but if everyone is afraid, no one would come out on to the streets," said 19-year-old Yana Aksyonova, explaining why she attended.