An attack on anti-terrorist police headquarters in Pakistan's largest city, Karachi, has left 20 dead and at least 100 injured.

巴基斯坦最大城市卡拉奇一座反恐警察总部遭遇袭击，30人死亡、100多人受伤。

Police say they exchanged fire with militants² trying to storm the Criminal Investigation³ Department building.

Then a truck laden⁴ with（充满，载满） explosives slammed into its boundary wall, detonated（引爆，爆炸） its load and almost completely destroyed the structure.

The blast could be heard across several miles of the city of 14 million people.

Eyewitnesses⁵ said the blast left a crater⁶ 12 metres (40ft) wide in front of the gutted⁷ building in Pakistan's financial and commercial capital.

TV footage showed bloodied⁸ victims being taken away on stretchers and dozens of security officers combing through the wreckage⁹.

"Over a dozen militants tried to storm the building," a police official who was inside the building during the attack told the BBC.

"An exchange of fire took place for at least 15 minutes. We then saw the pick-up truck trying to ram¹⁰ its way inside."

A government spokeswoman, Sharmilla Farooqi, said: "There are five policemen among the dead.

"We have reports that there may be some women police among the casualties because there was a women's police station inside the building."

One witness told the BBC that he had heard the exchange of gunfire before the explosion.

"I was playing tennis across the road at the Karachi Club when I heard gunshots and then a huge blast," said Ali Zaidi.

"Everyone started panicking and running toward the changing rooms. Some of my friends have been injured and have been taken to hospital."

The BBC's Shoaib Hasan, in Islamabad, says that CID officials and their offices - including this building - have been targeted in Karachi in the past.

Our correspondent adds that the latest attack comes a day after the same unit arrested several wanted militants in the city, said to belong to Lashkar-e-Jhangvi - Pakistan's most dangerous militant¹ group.

The group, which is closely linked to al-Qaeda, has been involved in a string of high profile attacks across the country.

It is unclear whether the suspects were being detained in the complex at the time of the attack but the BBC's Aleem Maqbool, in Islamabad, says that in the past, such detainees may well have been held and interrogated¹¹（审问，质问） in the CID compound.

Mohammad Aslam Khan, of the CID, told the BBC that he believed the arrested men were planning to carry out bombings on Shia processions（队伍，行列） in the city.