iStock/Thinkstock(MOSCOW) — A top Russian opponent of President Vladimir Putin was arrested and violently dragged into a van by police Sunday amid protests around the country against the lack of political competition in presidential elections this year.

Alexey Navalny, an anti-corruption campaigner who has become Putin’s most substantial political challenger, was arrested in Moscow as demonstrations in his support were held in cities around Russia.

“I was detained,” Navalny tweeted in Russian after his arrest. “It does not matter.”

He added, “You don’t go for me, but for yourself and your future.”

Navalny also tweeted a video of his arrest and photos from the protests.

He was recently barred from running for president because of a fraud conviction that is widely believed to be trumped up. In response, Navalny called for a “voter strike,” including protests and an election boycott.

Sunday’s demonstrations are the first major protests since Russia’s election season formally began and since Navalny was barred by authorities from running.

The protests were held despite authorities’ banning such rallies in Moscow, St. Petersburg and other cities.

Earlier Sunday, police broke in the door of Navalny’s office in Moscow, claiming there was a bomb threat inside. In the days ahead of the protests, police had repeatedly searched his offices in different cities and detained several organizers.

Last year, Navalny led a series of large protests, the biggest Russia had seen in half a decade. In March and June, marches against corruption ended with mass arrests, including more than a thousand detentions in Moscow alone. Navalny has built a major grassroots organization around the country, which he claims has 200,000 volunteers.

Protests began early Sunday in Russia’s far east, which is many hours ahead of Moscow. Video from the Siberian city of Novosibirsk appears to show a few hundred people marching with banners in ferociously cold temperatures.

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