'Enemies of Pakistan who want to destabilise the country are coming here after their defeat in Swat,' Interior Minister Rehman Malik told reporters. 'There is a war and this is a war for our survival,' he added.
Pakistan's military has been locked in a month-long offensive against Taleban militants in three regions of the northwest, which the authorities say has killed around 1,190 extremists and sent 2.4 million people fleeing their homes.
Prime Minister Yousuf Raza Gilani condemned the blast and blamed 'state enemies' for the carnage, as he expressed his condolences for the loss of life.
The chief of Lahore's city administration, Sajjad Bhutta, said 23 people were killed in the attack and around 250 others wounded.
Police and witnesses said 30 to 35 policemen were trapped under the rubble.
Lahore police chief Rathore said he ordered no one to be discharged from hospital without police verifying the credentials of the injured, amid suspicions that three assailants managed to slip away.
Lahore has been increasingly rocked by violent attacks.
On March 30, attackers armed with guns, grenades and suicide vests stormed a police training centre on the outskirts of the city, unleashing eight hours of gun battles and killing seven police cadets and a civilian.
That attack was claimed by Pakistani Taleban chief Baitullah Mehsud - a man with a US$5 million (S$7 million) bounty on his head offered by the United States - who threatened to carry out further attacks across the country. -- AFP