Russian police detained Leonid Gozman, an opposition politician, on Monday, his lawyer said, after a criminal case was opened over his alleged failure to inform the authorities swiftly enough about his citizenship of Israel.
"At the entrance to the Frunzenskaya metro station, he was detained by metro police officers," Gozman's lawyer, Mikhail Biryukov, said on Facebook.
Gozman was the last leader of the small Union of Right Forces political party, which brought together free-market reformers such as Anatoly Chubais, who has left Russia, and Boris Nemtsov, who was shot dead in 2015 close to the Kremlin.
Gozman had argued publicly that President Vladimir Putin has inflicted more damage on Russia by invading Ukraine than any other Russian leader since Josef Stalin, and that post-Soviet Russia had essentially died with the war.
Last month Gozman was officially listed as what Russia terms "a foreign agent" - a person who receives money from foreigners or is under the influence of foreigners.
He has been placed on a federal wanted list, the interior ministry said. It was not immediately clear why.