At least four people, including an Iraqi national and two women, were killed and six injured on Monday when a suicide bomber disguised as a security officer struck at the UN food agency's office here, amid Taliban's warning of launching fresh strikes in Pakistan to avenge US drone attacks against them.
The bomber, who was disguised as a paramilitary Frontier Corps personnel, entered the heavily-guarded World Food Programme office in Sector F-8 after telling a private security guard that he wanted to use the toilet, Interior Minister Rehman Malik told reporters.
The police said the bomber blew himself up in the lobby of the WFP office, situated in the heart of Islamabad.
An Iraqi national and two Pakistani women working for the WFP were among the four people killed in the blast. Malik said six Pakistanis were also injured.
Malik warned that the local Taliban, under pressure due to military operations being conducted in the Swat valley and the tribal areas, could carry out more suicide attacks.
"Don't forget that the action we have taken in Swat and North and South Waziristan has broken their backs. They are like wounded snakes and they held a meeting five days ago and decided to carry out attacks in important places to put the government and people under pressure," he said.
Arrested Taliban leaders too revealed that the group had deputed "some people for suicide missions," Malik said. "They have devised their strategy and I believe there could be a few more attacks in the coming weeks."
The legs and pieces of the skull of the suicide attacker had been found after he blew himself up in the lobby of the WFP office, Deputy Inspector General of Police Bin Yamin said.
The blast devastated the reception and nearby areas and smoke could be seen billowing out of the WFP building.
UN officials and people in nearby buildings were asked to evacuate the area after the blast, which occurred at 12.15 pm, local time. About 80 people worked in the WFP office.
The UN also closed all its offices in Islamabad and Rawalpindi till further notice.
No group claimed responsibility for the attack. However, Taliban spokesmen had recently said militants would carry out a fresh wave of suicide attacks to avenge the killing of their chief Baitullah Mehsud in a US drone attack in August.
Malik said the federal government had issued several alerts over the past two weeks after receiving inputs from intelligence agencies about possible terrorist attacks in Islamabad and different places of Punjab, Sindh and Balochistan provinces.
He said there were also alerts that the attackers could strike in the guise of uniformed personnel or by using government vehicles.
Security will be further enhanced after today's attack, which was aimed at "destabilising and bringing a bad name to Pakistan", he said.
A probe will be conducted by the police, the Federal Investigation Agency, the Intelligence Bureau and the Inter-Services Intelligence to fix responsibility for today's attack, Malik said.
Officials said the police had detained several private security guards and were questioning them about the incident.
Footage from the WFP office's close circuit television system will also be part of the probe.
The WFP office is located a short distance from the Zardari House, the private residence where the ruling Pakistan People's Party chief Asif Ali Zardari lived before becoming the country's President, offices of the police force and the district administration and courts.
The WFP office and other UN organisations in Islamabad have been on high alert following intelligence reports that they could be targeted by militants. Reports said the WFP office had received threats on three occasions, but this could not be independently confirmed.
Following the attack, UN employees across Pakistan were asked to restrict their movements and not to use their mobile phones, TV news channels reported.
Malik said all UN offices and foreign missions in Islamabad had been asked to move inside the heavily guarded Diplomatic Enclave due to security concerns.
President Zardari and Prime Minister Yousuf Raza Gilani strongly condemned the attack at the WFP office and the loss of life.
In a message, Zardari said Pakistan could not be deterred in its efforts to fight terrorism and will continue its quest to usher in peace by eliminating terrorists. Zardari sought a report on the incident and said the perpetrators will not go unpunished.
In a separate message, Foreign Minister Shah Mahmood Qureshi said the killing of innocent people has no justification and such "barbaric, inhuman and un-Islamic terrorist acts only strengthen our resolve to fight terrorism with more vigour".
US Ambassador Anne W Patterson too condemned the bombing at the WFP office, saying: "Senseless acts of violence against people who help feed the poor and hungry are an attack on Pakistani society. Such cruel acts expose the true nature of the terrorists' agenda."The WFP has been providing vital food assistance to as many as two million Pakistanis displaced by the conflict in the Swat region, she said.