Gunmen sprayed a van with bullets, killing five female teachers and two aid workers, but they spared a child they took out of the vehicle first.
The director of the group that the seven worked for said he suspects it may have been the latest in a series of attacks targeting anti-polio efforts in Pakistan. Some militants oppose the vaccination campaigns, accusing health workers of acting as spies for the US and alleging the vaccine is intended to make Muslim children sterile.
Last month, nine people working on an anti-polio vaccination campaign were shot and killed. Four of those shootings were in the north-west where yesterday's attack took place.