JOIN USPak Navy HQ attack kills two naval policemen
The bomber approached the naval headquarters complex on Margalla Road, a key thoroughfare, on foot at 1.30 pm, and detonated his explosives when naval policemen deployed at the gate became suspicious and tried to frisk him.
"He was trying to enter the naval headquarters, and when the guards tried to check him and take off his coat, he blew himself up," Deputy Inspector General of Police (operations) Bin Yamin told reporters.
The naval policeman who tried to frisk the bomber was killed instantly while another died later in hospital.
Thirteen others, including four naval personnel and nine civilians, were injured.
A six-year-old boy who was passing the area sustained severe head injuries and was rushed to a nearby hospital for surgery.
Witnesses said the bomber was aged about 17 to 18 years.
No group claimed responsibility for the assault though Pakistani Taliban have been blamed for a series of bombings and suicide attacks, many of them targeting security forces.
Security forces, including elite commandos, cordoned off the naval headquarters after the blast as investigators gathered the body parts of the bomber.
Debris lay strewn all over the road in front of the naval headquarters. A few cars were also damaged by the blast.
A witness said he had seen the bomber alighting from a grey coloured car near the naval headquarters complex.
The driver of the car then tried to flee from the area.
"But the driver turned the vehicle towards the wrong side of the road and hit my car as I was waiting at a traffic light," the witness said.
The bomber was stopped at the outer-most security cordon, naval spokesman Captain Mobeen Bajwa told reporters.
The navy and police are jointly investigating the incident.
Footage captured by a CCTV camera will be helpful in the probe, Bajwa said.
In the past few weeks, militants and suicide bombers have targeted several security facilities, including the army's fortified headquarters in Rawalpindi, Federal Investigation Agency office and police training centres in Lahore and the Inter-Services Intelligence agency's provincial headquarters in Peshawar.
Dozens have died in these attacks.
The Taliban have claimed responsibility for many of the attacks on the security forces, which began after the army launched operations against militants in South Waziristan tribal region in October.
Interior Minister Rehman Malik, who sought a report on the incident from the Islamabad police chief, said terrorists cannot deter the government's resolve to fight extremism in all its forms.
He directed police to further strengthen security in Islamabad.
Describing militants as "hired killers," Malik said they were targeting security forces to demoralise them.
However, the people are united and the militants will not be spared, he added.