Russian police raided the Moscow headquarters of opposition leader Alexei Navalny on Sunday after his supporters began a day of nationwide protests, calling for a boycott of what they said would be a rigged presidential election in March.
Police forced their way into Navalny`s office using power tools, citing reports of a bomb threat, an online feed run by Navalny`s supporters showed.
Navalny also wrote on Twitter that he has been detained soon after joining a rally in Moscow on Sunday.
Меня задержали. Это значения не имеет. Приходите на Тверскую. Вы не за меня выходите, а за себя и своё будущее.
Navalny has been barred from running in the March 18 election which polls show incumbent president Vladimir Putin is on track to easily win. Though Navalny says he knows Putin will be re-elected, his spoiler campaign is aimed at lowering voter turnout to try to take the shine off a Putin win.
Six of Navalny`s allies were detained during the police raid, OVD-Info, an independent monitoring group, said. It said they were among more than 60 people detained across Russia by 1300 Moscow time.
Police shut down a TV studio at Navalny`s office during the same raid which had been broadcasting online news bulletins, but another studio in a different location continued to operate.
In the Urals city of Yekaterinburg, just under 900 miles (1448.41 km) east of Moscow, around 1,000 protesters gathered in temperatures of nearly -10 Celsius (50 Fahrenheit) to back Navalny`s boycott call.
"No election? No to elections," a placard being held by one young man read. Other protesters waved Russian flags or red and white placards calling for a boycott.
"We don`t yet have the right to vote," Masha, 16, who declined to give her surname, told Reuters. "But we need to think about the future and we want to live in a country where there will be honest elections."
Yevgeny Roizman, the city`s opposition-minded mayor, said he backed a boycott. "When you see injustice and lies and you can`t change the situation you can at least not take part in it."
Navalny's supporters said they expected thousands of people to take part in similar demonstrations in 118 towns and cities.
"Your own life is at stake," Navalny said in a pre-protest video. "How many more years to do you want to live with these thieves, bigots and creeps?"
It was unclear where Navalny was, but a group of police officers was stationed near his home. Navalny said he planned to attend the Moscow protest later on Sunday.
Police warned beforehand they would harshly suppress any illegal protest activity and authorities refused to authorise events in Moscow and St Petersburg, the country`s two biggest cities, raising the possibility of clashes.
A Reuters reporter saw a heavy police presence in central Moscow ahead of the protest, with a command centre and buses filled with policemen parked on side streets.
Navalny, a lawyer who has campaigned against official corruption, was barred from running for the presidency by the central election commission in December over what he said was a trumped-up suspended prison sentence.
The United States and the EU criticised the decision.
Putin, who has dominated the Russian political landscape for nearly two decades, described U.S. criticism of the election commission`s decision as crude interference in Russia`s internal affairs and suggested Navalny was Washington`s pick for the presidency.
Polls show Navalny had scant chance of beating Putin, but Navalny says the system is rigged against political opponents like himself which makes polls meaningless.