Prominent Russian opposition figure Ilya Yashin was arrested in Moscow on Monday, according to reports.
Irina Babloyan, a journalist and a host at the now defunct Ekho Moskvy radio station, said Mr 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,” Ms Babloyan said on the Telegram messaging app.
Mr Yashin, who has previously criticised Putin’s invasion of Ukraine, posted a tweet on Tuesday morning which stated he was on his way to a court hearing that “apparently will formalise 15 days of detention for me”.
Lawyer Vadim Prokhorov, who has represented many Russian opposition figures, said Mr Yashin was in police custody for allegedly disobeying a police officer.
“I’m not allowed to visit the (Moscow) Luzhniki Police Department to (see) the detained Ilya Yashin,” he said in a statement on his Facebook page.
According to news agency Reuters, there was no confirmation of his detention by Russian authorities.
Mr Yashin’s arrest is the latest in a long-lasting crackdown against critics of the Kremlin. The highest profile of these, Alexei Navalny, is currently 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.
Mr Yashin, who represents Moscow’s Krasnoselsky district, is an outspoken critic of the war.
“I am staying in Russia," he said on social media a month after the war.
“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.”