Police raid opposition leader Navalny's office

"Right now a search is going on in our Saint Petersburg headquarters," Navalny wrote on Twitter, posting a video of uniformed police and non-uniformed officials with his staff.

The charismatic politician, who has called a major protest on January 28, is urging voters to boycott the March election in which President Vladimir Putin is expected to win a fourth Kremlin term.

Navalny himself has been barred from standing in the election because of a fraud conviction he says was politically motivated.

His campaign offices around the country are gathering support for a poll boycott, but supporters say his campaign workers have come under intense pressure from the authorities.

The coordinator of the Saint Petersburg office, Denis Mikhailov, told AFP: "They are seizing computers, laptops and printed materials. They said they received a signal that we are distributing some dissident leaflets and that's the reason for the seizure."

Mikhailov added that he did not know what leaflets the police were referring to.

Navalny's campaign press secretary Ruslan Shavedinnov told AFP that "in the last two days there have been searches in 11 offices, they are taking away equipment and leaflets supposedly calling for a boycott."

Shavedinnov added that as he was speaking police had arrived at a 12th campaign office in the town of Izhevsk in the Urals region.

"We link this to the January 28 protest. The authorities are afraid of a large number of people on the streets and are trying to hinder us."

The campaign office's Twitter account said that police "have chucked out everyone except the coordinator (and) seized equipment, turned off our security cameras and covered the windows... so we cannot film."

Navalny wrote on Twitter that the authorities "are afraid of a boycott by voters. That means it's the right thing to do. Join us."