Prominent Russian opposition politician Ilya Yashin was detained in Moscow on Monday, a lawyer for opposition figures and a Russian journalist said on their social media accounts.
Irina Babloyan, a journalist and a host at the now defunct Ekho Moskvy radio station, said Yashin was detained while the two were walking together.
"I was walking with my friend, Ilya Yashin, in the park ... The police came and took Ilya away," Babloyan said on the Telegram messaging app.
Lawyer Vadim Prokhorov, who has represented many Russian opposition figures, also said Yashin was in police custody for the alleged administrative violation of disobeying a police officer.
"I'm not allowed to visit the (Moscow) Luzhniki Police Department to (see) the detained Ilya Yashin," he said on his Facebook page.
Reuters was not able to independently verify the reports. There was no official confirmation of the detention from Russian authorities.
Yashin's detention is the latest in a wider and long-lasting crackdown against opponents of the Kremlin. Opposition politician Alexei Navalny is the highest-profile Kremlin critic to be jailed, serving an 11-1/2 year sentence.
Since the start of the Russian invasion on Ukraine in February thousands of people have been detained at protests in dozens of cities across Russia.
Yashin, a municipal deputy for Moscow's Krasnoselsky district, is an outspoken critic of the war which the Kremlin calls a "special military operation".
"I am staying in Russia," Yashin tweeted on March 7. "I have said before and I keep repeating: Russians and Ukrainians should not be killing each other. If I am destined to end up in prison for anti-war speeches, I will accept it with dignity."
(Reporting in Melbourne by Lidia Kelly; Editing by Stephen Coates)