Ukraine has stripped Viktor Medvedchuk — a former oligarch and a close friend of President Vladimir V. Putin of Russia — of his Ukrainian citizenship, the government says, in an announcement that highlights Kyiv’s effort to excise the influence of prominent pro-Moscow politicians within the country.
Mr. Medvedchuk, a former deputy speaker in Ukraine’s Parliament and a onetime presidential adviser, was handed over to Russia in September as part of a prisoner swap. The authorities in Ukraine had captured him in April after he fled house arrest while awaiting trial on treason charges in a case initiated last year.
His influence in Ukraine was such that his name surfaced in the U.S. investigation into Russian meddling in the 2016 American elections. Mr. Medvedchuk was a client of Paul J. Manafort, the Republican political consultant who advised pro-Russian Ukrainian politicians before becoming chairman of Donald J. Trump’s presidential campaign.
President Volodymyr Zelensky of Ukraine said in an overnight speech late Tuesday that the decision to end Mr. Medvedchuk’s citizenship was based on a report by the country’s security services. “If people’s deputies choose to serve not the people of Ukraine, but the murderers who came to Ukraine, our actions will be appropriate,” Mr. Zelensky said.
Russia’s invasion has made national survival the overriding focus of Ukraine’s politics, and, as a result, has closed the space for agents of Moscow’s influence who for decades have played a role in Ukraine’s internal affairs.
Last spring, Ukraine seized some of Mr. Medvedchuk’s vast wealth, which had been amassed through energy deals with the Kremlin while he worked in support of Russian interests in Ukraine and beyond.
Mr. Zelensky said that the state had also stripped citizenship from three others: Leonidovych Derkach, Taras Romanovych Kozak and Renat Raveliyovych Kuzmin. All three were at onetime members of Ukraine’s Parliament and served pro-Russian interests.
Mr. Medvedchuk was handed over to Russia in September alongside Russian pilots and senior military officials in exchange for more than 200 Ukrainian fighters. Given that he has already been living in Russia for months, the immediate effect of the citizenship decision on him may be limited.
Mr. Putin visited Mr. Medvedchuk’s Crimea residence in 2012, and an official Kremlin photograph showed him with the Russian leader at a martial arts tournament in 2013.
Russian officials had previously played down their interest in Mr. Medvedchuk, despite his ties to Mr. Putin, who is the godfather of Mr. Medvedchuk’s daughter. A Kremlin spokesman in May had dismissed the idea of exchanging Mr. Medvedchuk for Ukrainian fighters, saying that he had “nothing to do with Russia,” according to the Russian state news media.
