The attack is the latest in what appears to be a scare campaign against political and civil activists in Russia's second largest city in the first months of 2018.

Masked men attacked an activist from Mikhail Khodorkovsky's Open Russia organization in St. Petersburg on Monday.

Open Russia activist Oleg Maksakov was beaten by two unidentified men at the entrance to his home, the organization’s spokeswoman Natalya Gryaznevich told the Mediazona news website on Monday.

Gryaznevich speculated that Yevgeny Prigozhin, a Kremlin-linked businessman charged last week with conspiring to interfere in the 2016 U.S. election, may be behind the latest string of attacks.

Prigozhin, known as “Putin’s chef,” was among 13 Russians to be charged last week for election meddling in an investigation by U.S. Special Counsel Robert Mueller.

“Prigozhin’s websites and [social media] groups are replete with lists of ‘enemies of the people’ with photos and home addresses of the activists,” Gryaznevich wrote on Facebook.

“Oleg [Maksakov] is on that list. I don’t want to fuel tensions, but anyone who finds themselves on these lists has to be more careful,” she said.

The Open Russia pro-democracy NGO, founded by exiled opposition figure Mikhail Khodorkovsky, was blacklisted by Russia’s Prosecutor General last April as an “undesirable organization.”