Officials in Pakistan say at least 11 people have been killed in a car bomb attack on a government building in the city of Lahore.
More than 60 other people were injured when a car laden with explosives drove into a building housing an anti-terrorist wing of the Federal Investigation Agency.
The agency has been the target of previous attacks.
The amount of explosives brought down a two-storey building, as well as damaging a nearby school.
The explosion came after security forces said they had arrested a senior al Qaeda commander.
The man has been named as Abu Yahya Azam, an Egyptian-American believed to be a close aide to Osama Bin Laden.
In the past two weeks Pakistani security services have captured a number of senior Taliban commanders.
Meanwhile, Pakistani security agents have arrested an American al Qaeda spokesperson wanted in the United States on a treason charge.
Adam Gadahn, a California-born convert to Islam, has appeared in al Qaeda videos posted on the Internet threatening the United States with violence.