"The picture as a whole, in general, is clear: the change, which took over in the amount of 17 people ... For unknown reasons, an explosion occurred," RIA Novosti quoted him as saying.
The Russian Ministry of Health previously confirmed the death of 16 people in a fire near Ryazan.
The last male surviving burned 80% of his body surface area also died.
The prosecutor's office organized an investigation into the incident.