Moscow - Thousands of Russians demonstrated across the country Sunday to protest at corruption, defying bans on rallies which were called by prominent Kremlin critic Alexei Navalny - who was arrested along with dozens of others.Navalny called for the protests after publishing a detailed report this month accusing Prime Minister Dmitry Medvedev of controlling a property empire through a shadowy network of non-profit organisations. The report has been viewed over 11 million times on YouTube but Medvedev has so far made no comments on the claims.Navalny, who has announced his intention to run for president in next year's election, has been rallying supporters in major Russian cities in recent weeks.In Moscow, Navalny called on supporters to walk along the main Tverskaya street, and people congregated on the nearby squares lined with dozens of police vans and rows of riot officers as a police helicopter hovered overhead."We have all seen the movie, it gives specific examples of corruption and there has been no reaction," said 26-year-old factory worker Nikolai Moisey."They steal and they lie but still people will be patient to the end. The protest is a first push for people to start acting."Police detained Navalny shortly after 14:00 (11:00 GMT) as he was walking to the protest, putting him in a police minibus, and the surrounding crowd briefly tried to block it from driving off shouting "Shame!" and "Let him out!""Guys, I am all right, go on along Tverskaya," Navalny tweeted from the van.Between 3 000 and 4 000 people filled Pushkin square, with some shouting "Russia without Putin", referring to President Vladimir Putin.They also shouted "Russia will be free" as police seized protesters who held up placards."The whole country is tired of corruption on such a scale," 50-year-old Natalia Demidova said. "Medvedev should be fired once such exposes come to light."'99 cities' Some cities have officially sanctioned Sunday's protest. In the Siberian city of Novosibirsk, about 2 000 gathered in the city centre carrying signs like "No to corruption," according to local news website Sib.fm."People came out even in cities where there have not been any rallies for years," Navalny said in a message shortly after the Moscow rally began.Some held up images of yellow rubber ducks, following reports that Medvedev has a special house for a duck on one of his properties.In Saint-Petersburg, about 4 000 people gathered in the city centre. "We're tired of the lies, we have to do something," Sergei Timofeyev told AFP. The Russian constitution allows public gatherings but recent laws have criminalised protests unauthorised by city authorities, who frequently refuse to grant permission for rallies by Kremlin critics.Local media estimated about 1 500 people turned out in each of the Siberian cities of Krasnoyarsk and Omsk.In most places authorities had not authorised the rallies , and some of those who turned up to protest were detained by police.In the far-eastern city of Vladivostok, about 700 people nonetheless turned up, local website Prima Media said, and a dozen of people were detained by the national guard.In the Urals city of Yekaterinburg, about 1,000 people turned up, according to local Znak.com website.Navalny said on his website that 99 Russian cities planned to protest, but that in 72 of them local authorities did not give permission, citing reasons ranging from street cleaning to a bell-ringing concert to rival events by various pro-Kremlin groups.Authorities had also pressured students not to attend, and some cities even scheduled exams on a Sunday, according to reports.