Witnesses and Romanian media have queried safety standards at the club.
They are concerned about the lack of an emergency exit and the use of flammable material to soundproof the building.
The three arrested men, aged between 28 and 36, were questioned for several hours on Monday about the fire, the AFP news agency reported. It said one of those being held is a barman with shares in several clubs.
None of those arrested has made any comment.
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