The corpses were uncovered on Monday in an apartment in the city of Tula “with signs of a violent death”, the Russian investigative committee said in a statement, adding it had opened a murder investigation.

The corpses of the five — three boys aged four, five and nine as well as their mother and their grandmother — had been unnoticed in the flat for over a a week, Russian news agencies quoted police sources as saying.

The ITAR-TASS news agency said it appeared that they had been beaten to death nine days ago and the apartment had been locked up ever since. The corpses were found in the bathroom.

“All the corpses were piled up on each other in the bathroom,” a local witness who saw the apartment after investigators entered told the RIA Novosti news agency.

All the corpses showed signs of being beaten on the head with a hard object, the witness added.

RIA Novosti said that neighbours called police after detecting an unpleasant smell from next door. There was no sign that the attackers had forcibly entered the apartment.

Russian Interior Minister Rashid Nurgaliyev has been informed of the crime and has dispatched team of investigators from Moscow to the scene.

The discovery recalls the horrific murder of 12 people last November in a village in southern Russia that exposed the criminal anarchy and incompetence of authorities in the country’s provincial fringes.

The victims of the massacre village of Kushchevskaya in the southern Krasnodar region were a well-off farmer, his wife and 10 guests they invited to celebrate a national holiday including four young children.