Powerful car bomb hits Lahore
Rescuers are searching the rubble of a police building in Lahore after a bomb attack killed at least 23 people and injured 200 in Pakistan's second city.
Gunmen reportedly opened fire on guards before detonating a car bomb which flattened the emergency response building at police HQ.
Nearby offices of the ISI intelligence service were also damaged.
The interior ministry chief linked the attack to Taliban insurgents whom troops are battling in the Swat valley.
"Enemies of Pakistan who want to destabilise the country are coming here after their defeat in Swat," Rehman Malik said.
"There is a war and this is a war for our survival," he added.
Previous attacks on Lahore, Pakistan's second-largest city, were also blamed on the Taliban.
'They started firing'
Rescuers speaking unofficially put the death toll at 35, although this figure is unconfirmed.
Sajjad Bhutta, a senior government official in Lahore, told reporters that a car carrying several gunmen had pulled up in a street between the emergency response building and the ISI offices.
"As some people came out from that vehicle and started firing at the ISI office, the guards from inside that building returned fire," he was quoted as saying by the Associated Press.
"As the firing continued, the car suddenly exploded."
Issam Ahmed, a journalist with the Dawn newspaper in Lahore who arrived at the scene about 20 minutes after the blast, told the BBC he could still hear shooting in the area.
A least two arrests were made.
Rescue workers were seen clambering over a pile of concrete which was all that remained of the emergency response headquarters.
They were able to drag out several of the injured. Semi-conscious policemen could be seen being carried out in blood-stained uniforms.
Debris was scattered on the road outside. Officials were seen rushing towards the buildings to cordon off the area.
The blast also destroyed several cars parked or standing on the main Mall road opposite to the police building.
Bulldozers and other heavy lifting equipment were brought in as many people were feared to be trapped under the debris.
Altercations also took place between members of the media and security personnel as the former tried to get in to the site of the blast.
I ran out of the building and saw a surreal huge ring of white smoke rise into air
Matthias Gattermeier
eyewitness in Lahore, speaking to BBC
'Surreal scene'
Zubair, a BBC News website reader in Lahore, described hearing the explosion: "I was sitting in my office on Lawrence Road [about 500m from the site] when a huge explosion rocked our entire building.
"Glass windows shattered to pieces and the ceiling came down on the floor. I ran outside the building to nearby Jinnah Garden. I could hear gunfire which lasted for about 10 minutes and then I saw ambulance and police rushed to the scene."
Matthias Gattermeier, an Austrian reader also in Lahore, said his office building had been shaken so hard he thought it would collapse.
"We first thought the explosion happened far closer by, but the blast was just so massive," he said.
"I ran out of the building and saw a surreal huge ring of white smoke rise into air. Within minutes police and military blocked the streets. Disaster units and emergency are going in and out in every minute. The streets are full of people."
Lahore, Pakistan's second-largest city, has seen bomb attacks with increasing frequency.
Weeks before a police college was attacked in March, with eight people killed, militants attacked the Sri Lanka cricket team in the city, killing six police guards.
BBC NEWS | South Asia | Huge blast rocks Pakistani city
Eyewitnesses: 'Everything shattered'
After a powerful car bomb exploded in the Pakistani city of Lahore, people in the vicinity of the blast told the BBC News website about the chaos and confusion that followed.
Zubair's office, a short distance from the blast site, was partially destroyed by the force of the explosion.
Pakistani security officials and volunteers gather in front of the destroyed police emergency response office building - May 27
The blast destroyed a police emergency response building
All the windows shattered and the pieces fell to the floor as the blast happened.
We all ran outside the building and there were sounds of gunfire. We were so scared. There is a garden right next to our office so we immediately went to the garden and hid ourselves there to escape the gunfire. It seemed to be very close by. We didn't see any gunmen - we ran to hide.
The ceiling on our top floor was partially collapsed and all the glass in the building, everything was shattered. The walls had cracks in them. It was terrible.
Because of the way the road curves we couldn't see the blast site itself but there was a circular cloud of smoke above the site.
People were running around outside because of the gunfire. They were running away from the scene because it all seemed so close.
Fasih Khan's office was just 100 yards from the blast site.
I'm really afraid you know. We have seen hell today. It's just too bad.
Thank God, I didn't see the body parts...there were gunshots
I'm just next to the Mall road. I was working and all of a sudden there was a blast. We just rushed downstairs. We thought it might be an earthquake but the guards told us there was a huge blast.
It was like something smashed on the buildings. All our windows shattered and we just ran downstairs.
Then we saw all the smoke around our heads. Then ambulances and sirens came. Thank God, I didn't see the body parts. The ambulances, police, the media were rushing towards the scene and there were gunshots.
Matthias Gattermeier describes the chaos amid the dust and smoke in the immediate aftermath of the blast.
The blast completely shook our office building. There is another building in front of us and the force was so great we thought that building had been blown up.
We went outside and saw massive white ring of smoke in the sky. Within minutes there were police, all the streets were blocked and emergency was coming in.
People close by just ran away, others were heading towards the scene. No one knew exactly where it happened because there was so much dust and smoke in the air that it covered the whole region.
BBC NEWS | South Asia | Eyewitnesses: 'Everything shattered'