"It was a car bomb... The blast was so powerful that the vehicle flew from one side of the road to the other side of the road", said city police chief Tariq Jamil. "It appears to be a suicide bomber".

The embassy and American Centres were closed to the public immediately after the blast, as were the consulates in Lahore and Peshawar, announced Lynn Cassel, a department spokeswoman, told a news agency.

Though no group claimed responsibility, but anti-terrorist experts said they suspect the Al-Qa’eda terrorist organisation that masterminded the 11 September attacks on New York and Washington have carried to day’s explosion.

The blast took place after the visit of American Defence Secretary Donald Rumsfeld, who was in the region to diffuse tension between India and Pakistan.

"No one among the consulate officials or staffers has been killed or injured in the blast", Home Secretary of Sindh Province, Mokhtar Sheikh said, as other sources have said some of the consulate guards had been either killed or wounded in the blast.

"However, we are still assessing the identity of those killed. According to witnesses, among the dead is a private security guard posted outside the US consulate", he said.

Another 20 people outside the consulate were wounded by the blast, which left a crater several feet deep, destroyed a guard post and part of a concrete wall surrounding the building.

A deep crater was blasted into the road immediately next to the perimeter wall and the vehicle exploded into pieces, some of which were thrown onto the other side of the road and into a park facing the consulate.

Shock waves from the car bomb damaged property in a one kilometre radius of the area, blowing out shop windows and car windscreens and leaving shards of glass carpeted on the ground.

The blast was detonated after the car bomb reached the corner of the compound, and the huge explosion that followed destroyed part of the perimeter wall of the consulate, but left the main gate intact.

More than a dozen cars in the immediate vicinity were badly damaged. A spokesman for the US embassy in Islamabad said they were still gathering facts on the incident before making any statement.

The US embassy ordered non-essential staff and families to leave Pakistan shortly after a March 17 grenade attack on a church in the diplomatic enclave of Islamabad, which left five died, including two Americans.

Friday's blast is the fourth attack this year apparently aimed at foreigners in Pakistan, after the kidnapping of American reporter Daniel Pearl in January and a grenade attack on a church in Islamabad in March, which killed five people, including three foreigners.

Westerners were targeted again when a car loaded with explosives ploughed into a minibus at the Sheraton Hotel in Karachi on 8 May, killing 11 French nationals and three Pakistanis working on the construction of a French-made submarine in the harbour.