New York  - UN Secretary General Ban Ki-moon on Monday condemned "in the strongest terms" the attack that killed three workers of the World Food Programme in Pakistan, calling it a "heinous crime."

"Such an attack is unjustifiable," Ban said. "This is a terrible tragedy for the United Nations and for the whole humanitarian community in Pakistan."

Ban said WFP and its workers have been assisting tirelessly the poor and vulnerable. A total of five people were killed in the suicide attack.

"My deepest condolences go to the colleagues fallen in the line of duty for noble causes and their families and friends," he said.

WFP said it closed its office in Islamabad following the attack. dpa