Russian opposition politician Leonid Gozman votes during a party meeting in Moscow, November 16, 2008. REUTERS/Sergei Karpukhin

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.

Since the Feb. 24 invasion of Ukraine, political dissent has become more dangerous inside Russia. Protesters are routinely arrested and public criticism of the war risks prosecution.

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.

Putin says what he calls his “special military operation” in Ukraine was essential as the West was using Ukraine to threaten Russia, and that he had to defend Russian-speakers against persecution.

Ukraine and its Western backers say Putin has no justification for the war and that he is bent on reconquering a neighbor that was long under Moscow’s thumb before tilting toward the West after the Soviet Union broke up in 1991.

Gozman was last month listed officially 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.

In his last public post on Telegram, Gozman said: “For those who want and can protest — be careful, remember that what was almost free yesterday — a small fine — can cost freedom today.”

“Only if you understand what you will have to pay with — go ahead, and may God help you. Everyone else — do not give up.”