Moscow, Russia - Russia has accused Ukraine of plotting the murder of political scientist Darya Dugina, the daughter of a major Putin ally killed in a car bombing on Sunday.

"The crime was prepared and committed by the Ukrainian secret services," Russia's security agency, the FSB, said on Monday, according to the Interfax agency. The FSB's claim could not be verified, and others have said a Russian partisan movement was behind the killing.

Ukraine had previously denied having anything to do with Dugina's killing over the weekend. The 29-year-old was the daughter of Putin confidante Alexander Dugin, an influential author and philosopher who is thought to be a source of ideas for Vladimir Putin's decision to attack Ukraine. She was also considered a fervent supporter of the war.

"Ukraine certainly had nothing to do with yesterday's explosion," Mykhailo Podolyak, an adviser to Ukrainian President Volodymyr Zelensky, was quoted as saying. "We are not a criminal state like the Russian Federation, much less a terrorist one." He later suggested on Twitter that the bombing was carried out by Russian "special services."

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Zelensky himself warned that "Russia may try to do something particularly nasty, something particularly cruel" this week in response to Dugina's death.

Earlier, a former Russian politician claimed that a previously unknown partisan movement was behind the fatal attack on Dugina.

In a video published on YouTube on Sunday, Ilya Ponomarev, who is now living in Ukraine, said that the attack "opens a new page of Russian resistance against Putinism. A new page - but it won't be the last."

Ponomarev said that a movement called the National Republican Army is responsible for the attack.