A spokesman for Pakistan's main umbrella Tehreek-e-Taliban faction claimed responsibility on Monday for a suicide attack that killed up to 13 people in Lahore.
A suicide car bomber destroyed offices used to interrogate suspected militants in Lahore killing up to 13 people in the latest attack on Pakistan's cultural capital.
More than 65 were wounded as buildings collapsed after the bomber tried to ram a car packed with up to 600 kilograms of explosives into the investigations unit in Pakistan's second city.
There were scenes of panic as volunteers and rescue workers dug with bare hands under the collapsed two-storey building and a severely damaged Muslim seminary, searching for survivors amid fears the death toll could rise.
Pakistan pointed the finger at Taliban-linked militants seeking to destabilise the nuclear-armed country of 167 million. A wave of similar attacks has killed over 130 people in Lahore over the last year.
More than 3,000 people have been killed in suicide and bomb attacks across Pakistan since July 2007. The attacks have been blamed on Al-Qaeda-linked militants opposed to the government's alliance with the United States.
"We had just assembled in our classroom when it looked as if hell had broken with a huge blast," Noor Mohammad, a student at the seminary told AFP.
A thick pall of smoke accumulated outside the window as wood panels broke into pieces, hitting and wounding students.
"There was panic as students, many of them carrying their injured friends, rushed to the exit in a bid to find a safe place," Mohammad said.
Flying glass also injured passers-by. A woman and her daughter were among the dead in the city of eight million. The wounded civilians were mostly office workers or parents dropping their children at school.
Prime Minister Yousuf Raza Gilani called on members of the ruling Pakistan People's Party in Lahore to donate blood for the wounded.
"It was a police special investigation unit that was targeted. The building was used to interrogate suspected terrorists," Lahore city police chief Pervez Rathore told AFP.
The blast gouged a huge crater out of the ground, crumpled roofs and littered the streets with tree branches. Bulldozers and other heavy-lifting machinery worked to clear mounds of rubble, witnesses said.
Police officials said 13 people were killed and 65 wounded, but Khusro Pervez, Lahore's top administration official, put the death toll at 12.
Eight government officials, including police, and four civilians, including a woman were among the dead, he said.
"It's plain terrorism... the same groups which are already operating in Pakistan. It is a suicide bomb. There is ample evidence," Pervez told AFP.
Police said 30 to 50 people were in the investigative building, used by police and intelligence agents, at the time of the attack.
"We have found the head of the suicide bomber. It was found about 500 metres away," said Model Town police official Ayyaz Saleem.
Interior Minister Rehman Malik blamed "hired killers who want to destabilise Pakistan" and blamed the Tehreek-e-Taliban Pakistan (TTP) faction holed up along the northwestern border with Afghanistan.
"In almost every blast there has been TTP involvement and they themselves have also claimed responsibility for attacks," he added.
The city's Jinnah Hospital declared a state of emergency, straining to cope with casualties as rescuers used seismic sensors to search for survivors.
The attack follows a recent decline in violence by Islamist militants in Pakistan after a significant increase in bloodshed in late 2009.
Pakistani officials had linked the reduction to the suspected death -- still not confirmed -- of TTP leader Hakimullah Mehsud and military offensives that have disrupted militant networks.
The military claims to have made big gains against Taliban and Al-Qaeda strongholds over the past year, launching major offensives in the northwestern district of Swat and the tribal region of South Waziristan.
Washington says militants use Pakistan's semi-autonomous tribal belt to plot and stage attacks in Afghanistan, where more than 120,000 NATO and US troops are helping Afghan forces battle the Taliban militia.