A massive explosion has ripped through a security compound on a busy commercial street in Pakistan's largest city, Karachi, killing at least 20 people.
Officials said 100 more have been injured, and the number of casualties may rise further.
The explosion occurred inside the compound of the Criminal Investigation Department.
The blast left a crater about four metres deep in front of the building, which was gutted and some parts of nearby buildings collapsed.
A witness says the blast shattered windows up to 2km away.
The Tehrik-e-Taliban Pakistan (TTP), claimed responsibility for the attack which a spokesman said was in retaliation for U.S. air strikes in the country's northwestern tribal areas.
The building is used to hold and interrogate a number of militants, including those from banned organisations. It was not immediately clear how many were inside at the time of the attack.