Thousands of Russians have taken to the streets of Moscow to mark one year since a major opposition protest ended in mass arrests.
Police said about 6,000 protesters were present at the start of Monday's rally. Al Jazeera's David Chater, reporting from Moscow, estimated the crowd at 20,000. Only up to 30,000 people were allowed by the government to protest.
"It looks like a very powerful protest and it looks like it's going to be full as much as the mayor of Moscow allows," Chater said.
Our correspondent said opposition blogger Alexi Navalny, who is facing charges of embezzlement by the government, is expected to address crowd.
"It's not the case yet that Putin has completely extinguished the spark of this protest," Chater said.
Hours before the protest began, a worker died after he was struck by acoustic equipment as he was helping to erect the stage for the event.
Monday's rally remembers the protests on the eve of Vladimir Putin's inauguration for a third presidential term that resulted in more than 400 arrests after scuffles with riot police.
The opposition hopes the latest rally will breathe new life into the protest movement following what observers say is the toughest crackdown on dissenters of Putin's 13 years in power.
More than two dozen people now face jail over their involvement in last year's rally, which took place in the same square as Monday's protest, just across the Moscow river from the Kremlin.
One activist has been jailed for four and a half years for purportedly using violence in the 2012 rally, while another has been sentenced for two-and-a-half years.
Pro-opposition writer Boris Bakunin, one of Russia's most popular novelists, said the new rally at Bolotnaya Square was the "last chance" for Russians to show the Kremlin they did not agree with its policies.
"If few people come to Bolotnaya on May 6, then the regime will see it as carte blanche from society: 'Put in prison whoever you want, we are not against it'," he wrote in his blog ahead of the rally.
Authorities have allowed to gather up to 30,000 for a demonstration until 17:30 GMT.
Prosecutors warned the opposition against any provocations including any attempts to hold a march through the city in addition to the rally, while police said it would deploy 5,000 personnel to oversee the event.
Putin last year reasserted his authority through tough legislation which requires NGOs receiving foreign aid to register as "foreign agents", expands the definition of treason and introduces steep fines for misdemeanours at rallies.
Also on Monday, the justice ministry said it was putting on hold the registration of several political parties including the liberal Popular Alliance.