Pakistani authorities on Friday accused the Taliban- and Al-Qaeda-linked insurgents for the Thursday's attack on the CID building in Karachi which killed 17 people. More than 140 have been injured in the blast and police believe that more than 1,000kg of explosives were used in the attack, making it the biggest blast ever to hit the country's financial capital.

Investigators are currently examining CCTV footage, while rescue teams are clearing the debris at the site. According to AFP, the attack, which took place in the 'Red Zone' in Karachi, was claimed by the Tehreek-e-Taliban Pakistan (TTP), an outfit linked to both Taliban and Al-Qaeda.

Police said gunmen drove a truck close to the Criminal Investigations Department (CID) building on Thursday evening, opened fire on the guards and later detonated a truck packed with explosives. The building holds several insurgents for interrogation.

Bombings across the country have killed more than 3,800 people in the country over the past three years. Geo TV reported that the metrological department measured the magnitude of the explosion at 1.3 on Richter scale.

The blast left two craters 15-feet deep in the ground. It also destroyed a nearby mosque and shattered windowpanes of many abutting buildings. Several government buildings, the US Consulate, and luxury five-star hotels were in close vicinity of the attack.

Over the past couple of days, Pakistani police have announced the arrests of activists of the proscribed Lashkar-e-Jhangvi, a group linked to Al-Qaeda. Six of the detainees were produced in the court hours before Thursday's attack. TTP spokesman Azam Tariq reportedly told AFP from an undisclosed location that the attack was to avenge the arrest and torture of his comrades.