Militants armed with guns and grenades stormed the offices of a US-based Christian charity in Pakistan yesterday, killing six aid workers in an attack blamed on Islamist rebels.

The gunmen stormed the World Vision building near the town of Oghi in the Mansehra district of North West Frontier Province (NWFP), where Taliban and Al Qaeda-linked militants have waged a deadly campaign.

The aid group condemned the attack as “brutal and senseless”, and indefinitely suspended all of World Vision’s operations in Pakistan, where the charity has about 300 staff.

World Vision said six Pakistani employees, including two women, were killed and seven others wounded when up to 15 gunmen arrived in pick-up vehicles and began firing on the aid workers.

“They gathered all of us in one room. The gunmen, some of whom had their faces covered, also snatched our mobile phones,” said World Vision administration officer Mohammad Sajid, who was in the office at the time.

“They dragged people one by one and shifted to an adjacent room and shot and killed them... After that one of them said: ‘It is enough, we should leave now’. While leaving they lobbed grenades.”

Rienk van Velzen, World Vision’s regional communications director, said by telephone from the Netherlands that all staff in the office were Pakistani.

“We have four male and two female staff members killed,” he said.

The organisation has operated in the area since October 2005, when aid workers flooded into the northwest after a 7.6-magnitude earthquake killed more than 73,000 people and left about 3.5 million homeless.

But many charities have left the area, as Islamist violence has soared. In February 2008, four aid workers with British-based group Plan International were killed in a similar gun and grenade attack in Mansehra town.