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MOSCOW — Russian police wrestled opposition leader Alexei Navalny into a police vehicle on Sunday, moments after he appeared at a rally to urge voters to boycott what he said would be a rigged presidential election in March.

Video footage posted on social media showed Navalny appear on Moscow's main thoroughfare to join several hundred supporters taking part in the protest a few hundred yards from the Kremlin. Authorities had said the protest was illegal.

He had only walked a short distance when he was surrounded by helmet-clad police officers. They wrestled him to the ground on the pavement, and then dragged him feet first into the patrol wagon, the video footage showed.

Задержание одного человека теряет малейший смысл, если нас много. Кто-нибудь, придите и замените меня pic.twitter.com/TODVdF5lEm — Alexey Navalny (@navalny) January 28, 2018

Navalny's personal Twitter feed carried a post to his followers saying he had been arrested. "That does not matter. Come to Tverskaya. You're not coming out for me, but for your future," the post said.

Earlier on Sunday, police forced their way into Navalny's campaign headquarters using power tools, citing reports of a bomb threat, an online feed run by Navalny's supporters showed.

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Demonstrations were reported throughout the country. Local news reports said about 1,000 Navalny supporters were marching in St. Petersburg.

The OVD-Info group, which monitors political arrests, reported scores of demonstrators had been detained at protests in cities including Murmansk, Ufa and Kemerovo.

Russian opposition leader Alexei Navalny moments before he was arrested while attending a rally in Moscow, Russia, Sunday, Jan. 28, 2018. Evgeny Feldman / AP

Several hundred demonstrators assembled in the Pacific port city of Vladivostok, complaining both of Putin's rule and of Navalny's exclusion from the presidential election.

"They took these elections away from us, they took away our votes. Our candidate was not allowed to run," said Vladivostok demonstrator Dmitri Kutyaev.

Navalny has been barred from running in the March 18 election because of a conviction in a fraud case which has been viewed as political retribution.

Polls show incumbent president Vladimir Putin is on track to easily win the upcoming vote. Though Navalny says he knows Putin will be re-elected, his boycott campaign is aimed at lowering voter turnout to try to take the shine off a Putin win.

The Kremlin says the election will be fair. They say Navalny and his supporters have minimal support and are irresponsibly trying to foment social anger which could lead to turmoil.

Navalny rose to prominence in 2009 with investigations into official corruption and became a protest leader when hundreds of thousands took to the streets across Russia in 2011 to protest electoral fraud.

A few years later, and after several short-term spells in jail, Navalny faced two separate sets of fraud charges, which were viewed as political retribution aimed at stopping him from running for office.

In his only official campaign before his first conviction took effect, Navalny garnered 30 percent of the vote in the race for Moscow mayor in 2013.