Islamabad, Oct 5: A daring suicide attack in the offices of the World Food Programme (WFP) today killed at least three people, one of them foreigner and wounded five others.

The attack set off ripples among security officials in Islamabad as this was for the first time that a bomber managed to enter the well-protected WFP building, which was being guarded by some 19 private security guards in addition to police and paramilitary Frontier Constabulory.

“It was a suicide attack and we are trying to ascertain how the attacker, who aged 26-32 years entered the building,”senior Islamabad police official, Bani Amin told reporters.

He added that one of the dead employees of the WFP was Iraqi national.

He said that police also found legs and a part of attacker's skull from the main lobby of the WFP offices, which were sealed off after the explosion as ambulances with flashing lights took away bodies and wounded persons.

The latest attack came amid repeated threats by Tehreek-e-Taliban Pakistan, which vowed to take revenge for death of their chief Baitullah Mehsud in a US missile strike on August 5.

Mehsud was accused of masterminding dozens of suicide attacks and bomb explosions mostly targeting security forces all over Pakistan.

More than 2,000 people have been killed in explosions and suicide attacks in the country since military assault on Islamabad's radical Red Mosque in July 2007.

Prime Minister Yousuf Raza Gilani strongly condemned the attack and ordered immediate inquiry.

Reacting swiftly, the United Nations announced closure of its offices in Pakistan until further orders.

“All UN offices in Pakistan have been closed until further order,” UN spokespersonSusan Manuel told The Telegraph.

She described the incident as “reprehensible” saying that terrorists targeted WFP, which is feeding up to two million people, displaced by recent military operations in the northwest.

She was also surprised how the attacker managed to entered the building, saying that the WFP building was well protected.