At least 1,000 people have reportedly been detained by Russian police at anti-war protests in 47 cities. Pictures and videos shared on Twitter show protesters chanting “no to war” and carrying signs.
Demonstrations have taken place in cities across Russia including in Moscow, St Petersburg, Novosibirsk and Tyumen.
Hundreds of people gathered at Pushkin Square in the capital, not far from the Kremlin.
Conservative Party MP Tom Tugendhat, who chairs the Foreign Affairs Committee, retweeted a video of the protesters as he praised their bravery.
He said: “Russians know they’re being dragged into a criminal war. This is extraordinary courage.”
Pictures show protesters being dragged away from rallies by officers dressed in riot gear.
ABC News foreign correspondent James Longman tweeted a video from the capital showing a heavy police presence.
He said protesters were being arrested and marched into trucks.
Mr Longman tweeted: “It takes a special kind of bravery to protest in Putin’s Russia, especially on the day he sends his country to war.”
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Wall Street Journal reporter Matthew Luxmoore shared a video from a protest in the captial.
He said: “A view of the protest in central Moscow this evening. Thousands across the country are risking serious repercussions to protest Putin’s attack on Ukraine. More than 850 people detained so far.”
Russian authorities have told people not to take part in anti-war protests.
In a statement, the country’s Investigative Committee said: “It should be remembered that holding a criminal record holds negative consequences and leaves a mark on the person’s future.”
Earlier on Thursday, a Russian opposition activist who called for anti-war protests in Moscow was detained by police.
Activist Marina Litvinovich wrote on Telegram: “I was detained on my way out of the house.”
The protests come as Moscow launched an invasion of Ukraine by land, sea and air early on Thursday.
Hundreds of Ukrainian protesters gathered outside Downing Street today as they called on the UK to do more to stop Vladimir Putin taking over their country.