The blasts triggered by Improvised Explosive Devices (IED) tied to two bicyles took place in the peak hour at two sites 100 metres apart outside a roadside eatery near Konark and Venkatadiri theatres in the area located on the Hyderabad-Vijaywada national highway in Cyberabad police limits.
A woman was among the 12 dead, said state DGP Dinesh Reddy, who said it was "definitely the handiwork of a terrorist network." Reddy said IEDs were used in the attack.
Union Home Secretary R K Singh said the near two simultaneous very powerful blasts indicate that it was a "terror attack".
Andhra Pradesh Chief Minister N Kirankumar Reddy said five-six of the injured were serious.
The twin blasts, described as dastardly by Prime Minister Manmohan Singh who announced a Rs two lakh exgratia to the kin of each of the victims, triggered a stampede-like situation with people trying to scamper for safety as it left a bloody trail.
The scene wore a gory look with severed body parts lying around. Footwear and various other objects were also seen indicating the desperation of the victims and the injured to flee the spot.
The Dilsukhnagar area is thickly populated and traffic jams are routine in the evenings with officegoers and students rushing home. Large numbers of people wait at the numerous bus shelters, eateries and shops in the area.
Eight people were killed in the first blast that took place at 6.58 PM near Konark theatre and three in the second that followed three minutes later.
Shinde said two bombs were placed within a distance of 100 to 150 metres and placed in two bicycles.
The injured have been rushed to various hospitals by ambulances and police and bomb disposal squads swung into action and began searches.
There were reports that the bomb blast could be heard two to three kms away from the site of the explosion.
Sources in the state-run Osmania General Hospital said of the around 30 injured people admitted some of them were in a serious condition. They said three bodies were received brought dead.
Official sources said 14 blast victims were admitted to private Yashoda hospital at Malakpet. In another private hospital, 18 injured persons were admitted.
S A Huda, Additional DGP (law and order) said the bomb blasts occurred at two places both in the Dilsukhnagar area falling within the Cyberabad Commissionerate.
Terrible scenes were seen at the hospital as blood soaked injured persons, some of them grievously, being treated and their relatives wailing.
Chief Minister N Kiran Kumar Reddy and Home Minister P Sabita Reddy also rushed to the spot.
The Dilsukhnagar area witnessed a blast in 2002 near a famous Saibaba temple in which two persons were killed and over 20 injured.