Putin critic Boris Nemtsov shot dead
Investigators gather near the covered body of Boris Nemtsov in central Moscow after the Putin critic was shot dead Reuters

Alleged members of an armed pro-Russian separatist group operating in eastern Ukraine have claimed responsibility for the killing of Russian opposition politician Boris Nemtsov in a video that made the rounds on YouTube and VKontakte, the Russian Facebook.

Three balaclava-clad men, who claim to be part of the pro-Russian Rusich militia, are seen holding assault weapons and claiming that "government are traitors and we are doing what they should have done".

"We, the military council of Novorossiya [Russian imperialistic reference to Eastern Ukraine] have made a decision to execute the order regarding the American traitor Nemtsov who for his whole life sold our country and our people, a monster who supported the Bandera henchmen who have destroyed our people in the Donbass," said a masked member with a distorted voice, according to a translation by Interpreter Magazine.

However, the leader of the militia Aleksey Milchakov, dismissed the video as fake and said his unit had nothing to do with the murder in an interview on LifeNews, a pro-government TV channel.

He said he believed the fake video was uploaded by the pro-Kiev Azov batallion's Misanthrope division as a provocation to discredit them. Milchakov added that members of his militia do not wear balaclavas. "Our faces are always open - we have nothing to fear, we are responsible for our words," he said.

The clip is being promoted on channels linked to pro-Russian separatists fighting in Eastern Ukraine.

A first-hand analysis of the speaker of the video show a Russian accent typical of those native to the Donetsk area, according to Interpreter Magazine.

Blogger Christo Grozev posted a version of the audio with readjusted speed.

Nemtsov was shot dead in Moscow on a bridge overlooking the Kremlin on 27 February. A fierce Vladimir Putin critic, the politician was working on a report on Russia's alleged direct involvement in the eastern Ukraine conflict - something the Kremlin has long denied.

Milchakov was a member of the Batman's battalion, which was disbanded after their leader Aleksandr Batman Bednov was killed in mysterious circumstances.