The explosion came from a car near the police building, said spokeswoman Nabeela Ghazanfar, adding it was unclear if the attack involved a suicide bomber.
She said three people were dead but a police officer, who asked not to be named, said at least seven had died, citing colleagues in the area. It was unclear how many of the dead were police. 
The blast was followed by rapid gunfire, said witness Ashraf Ali, who works at the press club nearby. He could see threeb odies lying in the street.
Television channels later said the firing had stopped.
Pakistan has suffered two major militant attacks in the past month. Sixty people were killed in an attack on a Shi'ite mosque on Jan. 30 in the southern province of Sindh, and another attack this month on a Shi'ite mosque in the city of Peshawar killed 20.
Militant groups said this was a response to the government's lifting of a moratorium on the death penalty for those convicted of terrorist attacks.
The moratorium was lifted after a Taliban attack on a school in the northern city of Peshawar killed 134 children and 19 adults.  

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