At least 1,312 Russians were detained by police during protests across the country against President Vladimir Putin's declaration of mobilization earlier on Wednesday, according to the independent OVD-Info monitoring group.
Detainees in several cities were being threatened with subpoenas to join the Russian military, OVD-Info added, further stating that most arrests were made in St. Petersburg and Moscow.
Hundreds gathered in the Russian capital, chanting "no war," "send Putin to the trenches" and "let our children live," the independent Moscow Times said, citing videos circulating on social media.
"Send [Russian President Vladimir] Putin to the trenches!"Russian protesters in Moscow
Putin announces mobilization of 300,000 Russian reservists
Putin announced a partial military mobilization in Russia of 300,000 reservists during a pre-recorded speech on Wednesday. The mobilization will begin immediately.
Only reservists will be called up, with a focus on those with experience, Putin said. The president added that militants in Luhansk and Donbas will be considered soldiers of the Russian Federation going forward.
The 300,000 reservists called up by Putin mark Russia's first mobilization since World War II.
Russian opposition calls for protests against Putin's 'criminal war'
Alexei Navalny, Russia's jailed opposition leader, called for protests nationwide for what he said was a "failing criminal war."
"It is clear that the criminal war is getting worse, deepening, and Putin is trying to involve as many people as possible in this," Navalny said in a video message from jail recorded and published by his lawyers. "He wants to smear hundreds of thousands of people in this blood," Navalny said.
Navalny's allies say Russian society does not support the mobilization drive.
"It's scary to watch how a mad bastard is destroying a country live on television," said Navalny's chief of staff Leonid Volkov, who lives outside Russia.
"In military terms, mobilization is hopelessly late and will not change anything in this lost war," he said. Russians should see it as a matter of "moral duty, survival and self-preservation" to push back against the Kremlin, he added.
Tzvi Joffre and Reuters contributed to this report.