The prosecutor in the Polish city of Koszalin said a leak in the bottled gas heating system probably caused the fire that killed five teenage girls in Poland.
The bodies of the 15-year-old victims were found on Friday in Koszalin, northern Poland, after firefighters extinguished a blaze in an adjacent room.
"The victims of this tragedy are 15-year-old children, girls celebrating a birthday," Interior Minister Joachim Brudzinski told broadcaster TVN24.
Prosecutors said carbon monoxide inhalation was the likely cause of the deaths.
A 26-year-old man employed at the location was hospitalised with burns.
Koszalin prosecutor Ryszard Gasiorowski said a leak in the bottled gas heating system probably caused the fire.
Earlier, firefighters blamed faulty electric wiring and substandard security procedures.
Gasiorowski said the fire probably broke out in the reception room and blocked the employee's way to evacuate the girls.
Autopsies will be carried out to confirm the cause of their deaths.
Prime Minister Mateusz Morawiecki has sent condolences to the victims' relatives.
The school that the teenagers attended was extending counselling and support to their friends and colleagues.
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