Heidenheim, Germany - Five men were found dead Thursday in a soot-filled apartment in the southern German town of Heidenheim and police were investigating the likelihood that they were killed by smoke from a gas heater.

"They probably died several days ago from inhaling the toxic fumes," said police spokesman Horst Baur.

The building's landlord called police about a week after another tenant had noticed soot on the windows and said the apartment had been quiet for days.

Police patrolmen opened the flat with the landlord's key, then called the fire brigade because of a smell of smoke. Firefighters in gas masks discovered the bodies in two separate rooms.

The police in Heidenheim, 75 kilometres east of Stuttgart, said there was no evidence of deliberate killing.

The registered tenants were of Russian origin. It was believed some of the victims were visitors. (dpa)