"We must find out who is legally accountable for this," Major-General Khamis Mattar al-Mazina told Reuters, adding that it was estimated about 20 workers shared each room.
Witnesses said many residents were treated for slight injuries and smoke inhalation, some at the site of the blaze which broke out in the early hours of Tuesday. The number of injured was not known.
Mazina said police were also looking into possible illegal subletting by the leaseholder.
They were examining safety measures at the house and trying to establish whether the building, which was divided into 42 rooms, had been extended without building permission. he added.
Sources close to the investigation said wooden panelling was used to create a second floor and dividers separated living spaces. They said the fire was believed have been caused by a faulty cooking stove.
