The blasts, within minutes of each other, took place yesterday in Ancholi, damaging shops and vehicles.
DIG East Javed Odho said the bombs were planted in motorcycles that were parked in the crowded area. He said that about 3 to 4 kilogrammes of explosive material was used in the explosions.
The Pakistani Taliban claimed responsibility for the blasts.
Tehrik-e-Taliban spokesperson Shahidullah Shahid said that these attacks were in retaliation for the November 25 violence in Rawalpindi which killed at least 11 people and the drone attack on November 21 in Hangu in which six persons were killed and at least eight others were injured.
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Pakistan Prime Minister Nawaz Sharif has strongly condemned the bomb blast.
"The Nation will never be intimidated by these acts of terror in Karachi. Law and writ of the state will take care of fear-mongers, responsible for such heinous crimes. We will make sure that terrorists and criminals are speedily prosecuted and justice is dispensed without fear and favour," a statement released by his office said.
Terming the blasts in Karachi a cowardly act of terrorism, he said "All institutions will have to work without fear and upholding professional competence for effectively addressing the menace of terror".