TTP spokesman Shahidullah Shahid claimed responsibility for the attack while speaking to Dawn News channel. He said it was a "revenge attack" for the killing of militants.
Taliban fighters were victims of targeted killings at several places in Khyber-Pakhtunkhwa province, he claimed. "Our defensive war will continue until an agreement is reached on a ceasefire," he said.
Teams representing the government and the TTP have held discussions on framing a roadmap for a dialogue but it is unclear whether the two sides will agree on a ceasefire.
According to initial reports, about 30 kg of explosives were used in the attack on the bus that was carrying more than 50 policemen. The rear of the bus was destroyed and the blast was heard from two kilometres away.
The TTP and other militant groups have carried out similar bomb attacks on police and paramilitary personnel in Karachi in the past.
