At least five people are dead after a suicide bomber blew himself up in the lobby of a United Nations building in Pakistan Monday.
   
The blast occurred at the headquarters for the World Food Program, shattering windows and leaving victims lying on the ground.
 
The explosion sent a number of people to the hospital with serious injuries and Pakistani officials said the death toll could increase.

"There was a huge bang, and something hit me. I fell on the floor bleeding," said Adam Motiwala, an information officer at the U.N. agency who was hospitalized with injuries to his head, leg and ribs.

The WFP was distributing food to poor Pakistanis, including some who suffered loss in a recent Pakistan army battle against militants in the Swat Valley. The organization said it will close its offices in Pakistan temporarily.

U.N. Secretary-General Ban Ki-moon called the attack "unjustifiable."

"This is a heinous crime committed against those who have been working tirelessly to assist the poor and vulnerable on the front lines of hunger and other human suffering in Pakistan," he told reporters from Geneva.

Islamabad was last attacked in June, when two police officers were killed. A luxury hotel in Peshawar was also attacked in June, killing two staff members.