A roadside bomb killed six police escorting polio vaccinators and a teenage boy in north-western Pakistan Wednesday, in second attack on health workers in two days, officials said.
A local police official said the bomb planted on a bicycle parked along a road exploded when the police van passed by, dpa reported.
At least 11 people were injured in the attack in Charssada district of Khyber-Pakhtunkhwa province, police chief Shafiullah Khan said.
The attack occurred one day after gunmen killed three health workers carrying out polio vaccinations in the southern city of Karachi.
No group claimed responsibility for the attacks, but Islamist militants had targeted vaccination teams workers in the past.
About two dozen health workers taking part in a UN-funded immunization campaign and police officials protecting them were killed by militants in the past year.
Insurgents accuse health workers of acting as spies for the United States, and claim the polio vaccine is intended to make Muslim children sterile.
The World Health Organization says Pakistan is the only country in the world where the number of new polio cases was on the rise in 2013.