The assault began at about 9 am when gunmen burst into the World Vision office in Ogi, a small town in Mansehra district, which was badly hit by an earthquake that killed 73,000 people in October 2005 and left 3.5 million homeless.
“They entered the building, set off a bomb and then opened fire,” a police officer said.
“We are deeply sorry we've lost staff members who were locals who were deeply committed to improving lives in Pakistan," said James East, a World Vision spokesman.
The attackers, at least 15 according to eyewitnesses, fled into a nearby forest without leaving a trace. Law enforcement agencies have surrounded the area and launched a manhunt.
On its website, World Vision describes itself as a “Christian humanitarian charity organization dedicated to working with children, families, and their communities worldwide to reach their full potential by tackling the causes of poverty and injustice.” Although motivated by Christian values, it is devogted to people of all faiths.
Northwestern Pakistan has been an al-Qaeda and Taliban stronghold for some time with the latter moving with impunity across the Pakistan-Afghanistan border.
Recently, the Pakistani government launched an offensive against them, but so far has had limited success.
Mansehra, which is outside the tribal areas, is generally peaceful but it has seen some minor attacks in the past.