Thousands of people were detained across Russia on Saturday, as protests swept the nation to demand the release of jailed Kremlin critic Alexei Navalny. Tens of thousands defied an official ban on Saturday's demonstrations, and the extreme cold, as police tried to break up the rallies with force. Amateur video in St. Petersburg showed the moment one woman was kicked to the ground. Navalny called on supporters to protest after he was arrested last weekend. That's shortly after returning to the country for the first time, since being poisoned with a nerve agent in August. In central Moscow, Reuters reporters estimated up to 40, 000 people had gathered in one of the biggest unauthorized rallies in years, though officials there downplayed the number. Protesters there chanted 'Putin is a thief', as well as 'Freedom to Navalny'. As a result, one monitor group says more than 3,000 were detained across about 100 towns and cities. Some of Navalny's political allies were detained in the days leading to the protests. Others, on the day itself. Navalny and his supporters hope the mass demonstrations will pressure the authorities to let him go. The ex-lawyer accused Vladimir Putin of ordering his killing, which the Russian president denies, and now faces years in jail. The West has called for Navalny's release, while denouncing the use of violence over the protests. There was no immediate comment from the Kremlin, who has called the rallies illegal.