An organizer of an upcoming march to commemorate slain Kremlin critic Boris Nemtsov has been severely beaten in Russia's Urals city of Chelyabinsk.

A member of the opposition PARNAS party, Aleksei Tabalov, wrote on his online blog that Vyacheslav Kislitsin was attacked by unknown men in Chelyabinsk on February 26.

According to Tabalov, Kislitsin was hospitalized with numerous wounds, a broken rib, and heart problems.

Tabalov quoted Kislitsin as saying that city police officers were among the attackers.

Tabalov says the attack was connected to the planned march to commemorate Nemtsov on February 27.

Nemtsov, a former deputy prime minister and vocal critic of President Vladimir Putin, was shot dead near the Kremlin on February 27 last year.

"We absolutely connect this attack to tomorrow's demonstration to commemorate Boris Nemtsov, of which Vyacheslav Kislitsin…is the organizer," Tabalov wrote.

The regional branch of the Interior Ministry did not immediately comment on the alleged attack. Kommersant cited an unidentified law enforcement source as saying that Kislitsin's claims, according to preliminary information, are inaccurate.

With reporting by Kommersant