The office of Plan, the leading international children's NGO, was attacked today by a group of armed men.

Three local Plan staff were killed and another was critically injured in the attack by a group of six to twelve men carrying guns and grenades. The men entered the office in Mansehra, North West Frontier Province, before opening fire indiscriminately and then setting off three explosive devices. The office building has burned to the ground.

Tom Miller, Plan chief executive, said: "Our primary concern is for our staff and the families of those hurt in the attack. We have immediately closed our operations across Pakistan and dispatched a security team to the area. Counselling will be provided for those affected by the tragedy."

Details of the attack are still coming in, including the total number of casualties.

The attack comes as a shock as Plan has deep roots in the Mansehra area has worked with the community for more than a decade. Most staff are locals.

Plan was given no specific warning of a threat to its staff or offices at this time. The motive for the attack is still unknown.

Plan works with local communities in Pakistan to provide education and other opportunities to children. Plan played a leading role in the relief effort following the 2005 earthquake.

Note to editors: Plan works with more than 3.5 million families each year throughout Africa, Asia and Latin America. Plan is committed to working with local communities to strengthen children's rights.