ISLAMABAD - A terror cell attacked the World Vision offices in northwest Pakistan on Wednesday, killing six staff members, including two women, and injuring at least five others.

All the victims were Pakistani, police officer Waqar Ahmed said.

Armed with hand grenades and automatic rifles, the terrorists stormed the offices in Oghi, a small town in the Mansehra district of the North West Frontier Province.

The area was badly hit by the 2005 Kashmir earthquake, which killed more than 80,000 people.

World Vision's Oghi office has provided aid for many of the earthquake's survivors and helped Pakistanis fleeing the fighting in the Swat Valley.

Staffer Mohammad Sajid said he was in the building when "more than 15 armed men" arrived in trucks and pushed their way into the offices.

"They gathered all of us in one room. The gunmen, some of whom had their faces covered, also snatched our mobile phones," he said.

CBN News spoke with George Ward of World Vision for more insight on the attack and what the ministry was doing in Pakistan.  Click play to watch.

"The dragged people one by one and shifted to an adjacent room and shot and killed them. We could see them firing," he said.

Pakistani terror groups, some affiliated with al-Qaeda and the Taliban, accuse Christian aid organizations of working against the tenets of Islam and hampering their efforts to raise the standard of living.

Since 2007, Pakistani terror groups have killed more than 3,000 people.

The Associated Press and the Herald Sun contributed to this report.