In the first suicide attack in the Pakistani capital in nearly two years, a teenage bomber blew himself up on Monday outside a private bank owned by an ex-finance minister killing at least one and injuring three others while two more blasts in the country's restive areas left three people dead and six wounded.

The bomber detonated his explosive vest when he was stopped by a security guard as he tried to enter the branch of Silk Bank at the market in Sector I-8 in the heart of the capital city, police officials said.

Islamabad Police chief Wajid Durrani confirmed the attack was carried out by a suicide bomber.

Muhammad Bashir, the guard who stopped the bomber, was killed and three others were injured, officials said.

Officials at the Pakistan Institute of Medical Sciences described the condition of two wounded as serious.

Durrani said police had found the head and body parts of the bomber. Other officials and witnesses said the bomber was about 18 to 19 years old, who was dressed in a shalwar-kameez and approached the bank on foot.

One witness told the media that he had seen the bomber get out of a fast-moving car that sped off after dropping him in the market. The explosion occurred less than two minutes later, he said.

Footage on television showed the facade of the private bank was destroyed by the powerful blast. All the windows were blown out and the ceiling collapsed. Pieces of metal and tangled wires hung at the entrance of the bank.

Police and rescue teams rushed to the area and pushed away people who gathered at the site due to fears that a second blast could be triggered there.

No group claimed responsibility for the blast yet.

Silk Bank is owned by former Finance Minister Shaukat Tareen.

Monday's suicide attack was the first in the Pakistani capital since December 2009, when a bomber attacked the navy headquarters, killing one person.

It came a day after three persons, including a teenage boy, were injured when an explosive device went off beside a road on the outskirts of Islamabad.

In another blast today, three Pakistani soldiers were killed and four others injured when a military convoy was targeted with a roadside bomb in the restive South Waziristan tribal region.

The bomb was detonated by remote control and destroyed a vehicle, officials were quoted as saying by TV news channels.

The soldiers were on a routine patrol when the convoy was attacked.

Separately, at least two persons were injured when a bomb went off near a police complex in Quetta city in southwest Pakistan.

The blast occurred near the Police Lines at Gulistan Road in Quetta, the capital of the restive Balochistan province, TV news channels quoted officials as saying.

The nature of the blast could not immediately be ascertained. The explosion damaged several nearby buildings.

A suicide attack on a police officer's home in the same area of Quetta on April 7 had killed a policeman and injured nine more.

The explosive device was attached to a bicycle that was parked on Gulistan Road near a police check post, officials said.

Two passers-by were injured in the attack, officials said. Additional policemen, paramilitary troops and rescue teams rushed to the spot after the blast. The security forces cordoned off the area and launched a search.