Tens of thousands of Russian opposition supporters thronged the streets of Moscow on Saturday to keep up the momentum of their challenge to Vladimir Putin\'s rule four months into his new mandate. A diverse sea of protesters brandishing the red flags of socialism, nationalist tricolours or liberal slogans filled the avenue in Moscow named after the great Soviet physicist and celebrated dissident Andrei Sakharov. Some 40,000 people turned out for the \"March of Millions\", according to an AFP estimate, in line with organisers\' expectations but down on the massive first protests that first rocked Moscow in December and rallied over 100,000. Police and organisers gave vastly different estimates, accusing each other of not knowing how to count. Police said that 14,000 people joined the protest, but organiser and far-left leader Sergei Udaltsov saw at least 150,000. Waving nationalist flags, brandishing placards calling for early elections or wearing T-shirts in support of jailed punk band Pussy Riot, protesters hoped to build on the anger created by fraud-tainted elections and Putin\'s 12-year grip on power. The protest also tried to put a greater emphasis on social justice than past actions. \"Power to the millions not to the millionaires!\" read one slogan. Split between liberals, nationalists and the extreme left, the anti-Putin opposition has been struggling with its own divisions and accusations it lacks any coherent message beyond hostility to the Kremlin. The most charismatic opposition leader, anti-corruption crusader Alexei Navalny, told the protesters to prepare for a long haul to challenge Putin and turn up to rallies as if they were going to work. \"All that we are asking for is something simply called freedom, nothing more than equality, simply human dignity. \"No one will give us freedom except for ourselves. Hope and perseverance will bring us victory,\" he declaimed to cheers from the crowds.  Udaltsov, the leader of the radical Left Front, told the crowds: \"We must gradually conquer the streets. We are not leaving!\" Sporting dark sunglasses and a black bomber jacket, he urged supporters to wear shades to show their hatred of the authorities. The march was given extra impetus by the expulsion from parliament of anti-Putin deputy Gennady Gudkov over alleged conflicting business interests, in what the lawmaker\'s supporters said was crude revenge for opposing Putin. To some of the biggest cheers of the afternoon, Gudkov warned the authorities that if there was no reform \"they will either end up standing in blood, or they will be overthrown\". It is also the first mass action since the sentencing of three members of Pussy Riot to two years in prison for an anti-Putin protest in an Orthodox cathedral, which has become a rallying cause for many in the opposition.  Protester Anna Roskina, 33, a psychologist, held a banner saying \"Freedom for Pussy Riot! Freedom for us all!\" Police, who had warned of possible \"provocations\" at the rally, said 7,000 members of the security forces were deployed to ensure order. There was also a more light-hearted touch, with some protesters mocking Putin\'s recent \"birdman\" stunt, in which he flew a hang-glider to guide rare cranes on their winter migration. One protester dressed up in a white suit and a helmet of the kind worn by Putin with the slogan \"I teach cranes to fly\" written on his back.  \"We have shown that not all the birds fly behind the one who calls himself the alpha-crane,\" quipped opposition youth leader Ilya Yashin. The opposition is also enraged over the charging of 16 people -- 12 of whom are detained -- in a probe into crowd violence at a mass protest on May 6 just ahead of Putin\'s inauguration. Thousands-strong protests also took place in other major regional centres but relatively weak turnouts again underlined that the protest movement is a Moscow-generated phenomenon. Some 2,500 people turned out for the opposition protest in the second city of Saint Petersburg, an AFP correspondent said, while 800 people rallied in the Urals city of Yekaterinburg. But a protest in the Far East city of Vladivostok only mustered around a few dozen people, police and organisers said.