Twelve people, including four children, have been found suffocated and stabbed to death in a suspected mass murder in a house in southern Russia.

Investigators made the horrific discovery on Friday in a two-storey house in the village of Kushchevskaya in the southern Krasnodar region, the investigative committee of prosecutors said in a statement.

"According to preliminary information, the death of a young child was caused by toxic gas and another was strangled. The deaths of the other 10 were caused by multiple stab wounds," it said.

Traces of fires had been found in the house, it added. All of the victims had received between three and 10 stab wounds.

Initial reports had said that all 12 had been killed in a fire in the house but the new statement confirmed that fire was not the immediate cause of death.

The local branch of the emergencies ministry said in a statement on Russian news agencies that its employees had not been called out to fight any fire in the area.

The committee said it has opened a murder investigation, describing the crime as being of "particular brutality".

The motive remains a mystery and further details on the circumstances were not immediately available.

The Krasnodar region lies just north-west of Russia's troubled Caucasus mountains which has been plagued by Islamist militant violence and revenge murders over the last years, but it was unclear if there was any link.

The investigative committee statement said that owing to the gravity of the crime the case had been handed to the top investigative body for the region of the Caucasus and southern Russia.

- AFP