Rescue workers and residents search for survivors in the rubble of a police building hit by a suicide bomb blast in Lahore. (Mohsin Raza/Reuters)A suicide car bomber Monday struck a building where police interrogate high-value suspects in Pakistan's eastern city of Lahore, killing at least 12 people and wounding 61 more, including women taking children to school, officials say.

The attack broke what had been a relative lull in violence in Pakistan, where militant groups revile the government for its alliance with the U.S.

It also showed that insurgents retain the ability to strike the country's heartland, far from the Afghan border regions where al-Qaeda and the Taliban have long thrived, despite army offensives aimed at wiping them out.

No group immediately claimed responsibility, but suspicion fell on the Pakistani Taliban and allied militant groups. Those groups are believed responsible for a wave of attacks that killed more than 600 people starting in October, including several in major Pakistani cities.

More recent attacks have been smaller and confined to remote northwest regions near Afghanistan.

The explosion went off outside a Punjab province police building, police official Zulfikar Hameed said. TV footage showed a huge crater in the ground where the blast originated. It appeared the suicide bomber rammed a car packed with as much as 600 kilograms of explosives into the building's perimeter wall, officials said.

"This place was used to interrogate important suspects, but presently there was no such suspect, but more than 40 staff were manning the place," Lahore police chief Pervez Rathore said.

'Pieces of the roof fell upon us'

Noorul Huda, a student at a nearby religious school, was in his first class when the blast shook the area, he told TV reporters.

"With the huge bang, blocks and pieces of the roof fell upon us and six of us were wounded," said the young man, who suffered a head injury that was covered by a bloodstained cloth.

"It was total chaos outside and people were running and crying for help."

Pakistanis in the neighbourhood had filed complaints urging authorities to move the unmarked interrogation facility out of the residential area so the street wouldn't become a target for an attack, said Mohammad Musharraf, who lives nearby.

"My whole house was shaken and I thought it was an earthquake," he said. "A window dislodged and fell on my son, fracturing his arm."

Police official Chaudhry Shafiq said of the 61 people wounded, several were in critical condition.

Much of the police building collapsed in the attack, leaving piles of bricks and metal, TV footage showed. Nearby homes and other buildings, including a mosque, also were damaged.

During the bloody wave of attacks that began in October — coinciding with a major army ground offensive against the Pakistani Taliban in South Waziristan tribal area — Lahore was hit several times.

In mid-October, three groups of gunmen attacked three separate security facilities in the eastern city, a rampage that left 28 dead. Twin suicide bombings at a market in Lahore in December killed nearly 50 people.