The Czech Republic has frozen the assets of two men and a news website it accuses of running an influence operation in Europe that supports “the foreign policy interests of the Russian Federation,” the country’s Foreign Ministry said in a statement.

The ministry identified the men as Viktor Medvedchuk, a high-profile, pro-Russian Ukrainian politician and the leader of the effort, and Artem Marchevskyi, a Ukrainian-Israeli citizen who allegedly ran the website, the Czech-registered Voice of Europe. Long known as an ally of the Russian president, Vladimir V. Putin, Mr. Medvedchuk was arrested in Ukraine and handed over to Russia in a prisoner exchange in 2022.

“We cracked down on a Russian influence operation that was directed by Viktor Medvedchuk directly from Russia,” Jan Lipavsky, the Czech foreign minister, said in a statement. “The aim was to spread pro-Russian narratives undermining Ukraine’s sovereignty while infiltrating the European Parliament.”

While the Czech authorities refused to provide immediate comment on how expansive the effort was or how richly financed, officials promised further revelations.

“Actions in other countries will follow,” the Czech prime minister, Petr Fiala, said on social media, adding that the recent actions were “the result of international cooperation.”

Citing unnamed intelligence sources, the Czech news media reported that politicians from Germany, France, Poland, Belgium, the Netherlands and Hungary had been paid by the Voice of Europe to promote Russian interests in the European Parliament.