At least 13 people have been wounded in a suicide bomb attack inside the main police complex in Pakistan's capital, Islamabad, police have said.
Police said the attacker managed to drive into the Police Lines compound before blowing himself up inside a building of the anti-terrorist squad.
The Taleban carried out the attack, a spokesman for the group told the BBC.
The attack comes just over two weeks after more than 50 people died in a suicide bombing at the Marriott hotel.
It was a huge blast, just like an earthquake
Amanat Khan, local resident
It also happened as parliament met in a special joint session for a second day for a classified security briefing on Pakistan's internal security situation.
The joint session of parliament was called to try to help form a national consensus on how to tackle Islamic militancy and the recent surge in suicide bombings.
The inspector-general of Islamabad Police, Asghar Raza Gardezi, told the BBC the suspected bomber had driven a green vehicle into the Police Lines complex shortly before midday and parked outside a three-storey building that houses the police's anti-terrorist wing.
The blast destroyed one end of the anti-terror squad building
He then got out of the car and entered the building, where he put a bag of sweets he claimed to be selling on the desk of a policeman, Mr Gardezi added.
Moments later, there was a large explosion which destroyed a corner of the building and left a large crater. Shoes were strewn among the rubble.
One police official told the BBC that at least one person had been killed in the blast, but this is not confirmed.
Amanat Khan, who was about 500m away from the blast when it happened, told the BBC that it caused panic on the streets.
"Everybody started running away from where the sound came. I saw black smoke rising and the sound of a building crashing down," he said. "It was a huge blast, just like an earthquake."
As well as housing the anti-terrorism building which was attacked, the Police Lines complex contains accomodation and training facilities for police. Senior police officials are based elsewhere.
Mr Gardezi said the authorities would be looking into why a civilian vehicle was allowed into the police compound in the first place, and how the bomber evaded security checks at the entrance.
Another police officer told the BBC that it had been fortunate that many of the officers stationed in the building had been guarding parliament and other areas of Islamabad at the time of the blast.
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