A suicide bomb attack on a World Food Programme (WFP) office in Islamabad that killed five people on Monday was a "heinous crime," United Nations Secretary- General Ban Ki-moon said.
"This is a terrible tragedy for the UN and for the whole humanitarian community in Pakistan," he said in a statement, condemning the bombing "in the strongest terms".
"This is a heinous crime committed against those who have been working tirelessly to assist the poor and the vulnerable on the frontlines of hunger and other human suffering in Pakistan," he said.
In a statement distributed in Geneva, the Rome-based WFP said four of the dead were staffers of the agency, three of them Pakistani and one, information and communications technology officer Botan Ahmed Ali, an Iraqi.
The three Pakistani dead were identified as Abid Rehman, a financial assistant, and two women -- receptionist Gulrukh Tahir and office assistant Farzana Barkat.
Josette Sheeran, executive director of WFP which is providing food assistance to some 10 million Pakistanis, 2 million of them displaced by conflict in the country's Swat Valley region, described the four as "humanitarian heroes."
The agency -- which is the main UN body fighting hunger around the world -- supports school meal programmes and supplies food to vulnerable people across Pakistan, including many who have lost their homes in natural disasters.