A homicide blast killed five people inside the lobby of the heavily protected U.N. World Food Program office on Monday in what is normally an extremely secure neighborhood of the capital known as sector F-8.

Two of the five killed by the blast were Pakistani women; an Iraqi national and a Pakistani man also died. At least five others were injured.

Minister of Interior Rehman Malik has said the attack was a homicide bombing and the bomber was wearing a uniform for Frontier Corps, a paramilitary service of the Pakistan security forces.

Within 20 minutes after the explosion a small stream of smoke could be seen billowing out one side of the two-story building that is completely incased with rows of massive wired-wrapped sandbags and a security perimeter of fencing and barbed wire.

The protection of the building was to prevent damage from a bombing out front, so with blast coming from inside, there were few signs of the attack on the surrounding buildings.

Just down the street from the blast site is the family home of President Asif Ali Zardari and the main Pakistan Naval complex is less than four blocks away. There are few other areas in Islamabad that would be considered more secure than inside a U.N. office in this part of Islamabad. In comparison to other recent attacks, the casualty figures of this bombing are small but the signal of where the attack took place is huge.

Two hours after the blast the U.N. announced it was closing all of its offices in the capital.

There has not been a terrorist attack in Islamabad for six months, but there have been numerous warnings of potential attacks. An internal U.N. security warning for its employees in Islamabad telling them to stay away from Western targets and public areas was forwarded to FOX News just at the end of last week.

Police officials told FOX News that several private security guards stationed in front of WFP office have been arrested and some WFP employees have been taken in for questioning.

Over the weekend the Pakistani Taliban vowed to increase suicide attacks across Pakistan in response to the killing of its former leader and a video recently broadcast showing his dead body.