Russian opposition activists say an organizer of a provincial march to commemorate the 2015 slaying of opposition politician Boris Nemtsov has been severely beaten.

The opposition is holding rallies across Russia Saturday to commemorate one year since Nemtsov, a former deputy prime minister, was gunned down just outside the Kremlin. Authorities in several Russian cities have denied the protesters permission to rally.

Opposition activist Alexei Tabalov said on Friday that Vyacheslav Kislitsin was beaten by unknown attackers in the morning outside the factory where he works. He said Kislitsin suffered a heart attack and a broken rib and has been hospitalized.

Saturday's protest is expected to be the biggest opposition rally in months.