A former policeman in Siberia who is one of Russia's most prodigious serial killers was convicted Friday of two more murders, pushing "the werewolf" killer's body count to 80.

Mikhail Popkov had previously been convicted of 78 murders carried out between 1992 and 2007, when he raped and killed women with an axe or hammer after offering them late-night rides.

The 57-year-old killed his victims sometimes in a police car, while he was off-duty around his home city of Angarsk near Irkutsk in Siberia. He was nicknamed "the werewolf" and the "Angarsk maniac" by Russian media.

The local branch of the Investigative Committee, which probes major crimes, said in a statement that Popkov was convicted Friday for premeditated murder and sentenced to an additional nine years and eight months in prison.

Investigators said he was responsible for murdering two women 1995 and that he had penned a full confession in prison where he is severing two life sentences.

Popkov had previously described himself as a "cleaner" purging his city of its prostitutes. Only two women survived his attacks.

Russia has seen some prolific serial killers. 

Police in December said they had arrested a man suspected of robbing and killing 26 elderly women between 2011 and 2012, after investigators carried out thousands of genetic tests.

Alexander Pichushkin - the so-called "Chessboard Killer" - was sentenced to life in prison in Moscow in 2007 for 48 murders, most between 2002 and 2006. 

He said he wanted to kill one person for each of the 64 squares on a chessboard, and crossed out a square for every kill.