The blast had occurred in Ghaas Mandi on the gambling parlour and took the lives of over 20 people.
The remote-controlled blast, in which two kilogrammes of explosive material was used, also left over 40 people injured in the locality known as Jinnahabad Lyari Quarters.
An internal rift had been cited as the reason for the blast.
However, after a one-month break, the den had reopened. Area residents had accused the police of taking money to let the illicit activity continue.
The CID will be holding a news conference this evening to give further details of the raid and arrests.
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