A fire broke out at an "Escape Room" game location in northern Poland on Friday, killing five teenage girls and injuring a man, authorities said.
A man was seriously injured by the fire but survived.
The girls, friends from one school class, were celebrating one of their birthdays.
In a follow-up tweet he demanded that the cause of the fire "must be fully explained".
Escape rooms, in which participants are locked in a room and must solve a series of puzzles in order to get out, are popular around the world. Prosecutors said a leaky gas container inside a heater most likely caused the fire.
Last night, four of the five victims were named on local news websites and social media as Karolina Barabas, Gosia Tymieniecka, Wiktoria Julia Pietras and Amelia Wieczorek.
Agencja Gazeta / Reuters Poland's Interior Minister Joachim Brudzinski said the girls were all 15 years old.
Earlier, national fire chief Leszek Suski said Saturday that electrical wiring at the lo cation was makeshift and too close to flammable materials.
A spokesperson for local firefighters, Tomasz Kubiak said the units responding to the blaze had to use specialized equipment and force their way into the "Escape Room".
Since Friday, more than 200 of Poland's 1100 escape rooms have been checked, revealing a number of safety flaws that needed to be immediately fixed.
"Security was not ensured and that led to the tragedy", Mr Suski said.
Koszalin Mayor Piotr Jedlinski said in a statement the city would enter a day of mourning, on Sunday, for the loss of the girls.
Prime Minister Mateusz Morawiecki spoke after holding a meeting in which officials discussed ways to improve safety at entertainment venues.
Poland's President Andrzej Duda sent his condolences to the victims' families on Twitter.