A suicide bomber rammed a car filled with explosives into a U.S. government vehicle in northwestern Pakistan today, killing two Pakistanis and wounding 19 others including two Americans, officials said.

The attack in the city of Peshawar was a vivid reminder of the danger U.S. officials face while working in Pakistan, especially in the country's northwest where Taliban and al-Qaeda militants are strongest. Insurgents have carried out scores of bombings in Peshawar in recent years, but attacks against American targets have been relatively rare because of the extensive security measures taken by the U.S. government.

Peshawar

The bomber struck the armoured vehicle after it left the U.S. Consulate in Peshawar and while it was travelling through an area of the city that hosts various international organizations, including the United Nations, said police officer Pervez Khan, who was part of the security escort for the vehicle as it moved.

The attack killed two Pakistanis and wounded 19 other people, said senior police officer Javed Khan.

Two Americans and two Pakistanis working at the U.S. Consulate in Peshawar were among the wounded, said State Department spokeswoman Toria Nuland, who called the attack a "heinous act."

The injuries to the Americans were not life-threatening, said a U.S. Embassy official, speaking on condition of anonymity because the information had not been officially released.

"We stand ready to work with Pakistani authorities on a full investigation so that the perpetrators can be brought to justice," said Nuland.

The charge d'affaires at the U.S. Embassy, Richard Hoagland, praised Pakistani security forces for saving the lives of the four consulate employees.

"In this dangerous world where terrorists can strike at any moment, we must all work together  Pakistanis and Americans alike  because we have a strong mutual interest in defeating terrorism," he said.

The car driven by the suicide bomber contained 110 kilograms of explosives, Pakistani police officer Abdul Haq said.

The blast ripped apart the SUV carrying the U.S. Consulate employees and triggered a raging fire. Rescue workers and local residents rushed to put out the fire and pull away the dead and wounded. All that was left of the SUV in the end was a carcass of blackened, twisted metal.

Resident 'looked back in panic'

Irfan Khan, a local resident, said he was at a nearby shop when the blast occurred.

"I quickly looked back in panic to see smoke and dust erupt from the scene," he said. "I ran toward the scene along with others and saw two vehicles destroyed and the larger vehicle on fire."

One dead person was on the ground near the SUV, and a foreigner was injured, said Khan.

"We put the injured man and the dead body in a private vehicle," said Khan. "There were more injured in the surrounding area too."

Another eyewitness, Wajid Ali, said he helped put another seriously wounded foreigner into the vehicle.

But another vehicle arrived, presumably from the U.S. Consulate, and took away the wounded foreigners, said Javed Khan, the police officer. Some of the policemen escorting the U.S. vehicle were also wounded in the attack and their vehicle was damaged, he said.

No group has claimed responsibility for the attack, but suspicion will fall on Taliban and al-Qaida militants who have long had their sights set on the United States. American drones have fired scores of missiles at the militants' hideouts in Pakistan in recent years, and Washington has given the Pakistani military billions of dollars to fight the extremists.

American assets targeted in past

Islamist militants have targeted American assets in Peshawar, which is located some 135 kilometres from the capital of Islamabad, on several occasions in recent years.

They unleashed a car bomb and grenade attack against the U.S. Consulate in Peshawar in April 2010 that killed four Pakistanis, including three security personnel and a civilian. In August 2008, the top U.S. diplomat at the consulate survived a gun attack on her armored vehicle. Three months later, gunmen shot and killed an American in Peshawar as he was travelling to work for a U.S.-funded aid program in the region.

Despite the danger, Peshawar has long been a vital hub for U.S. interests in the region. It is the capital of Khyber Pakhtunkhwa province and is located on the border of Pakistan's semiautonomous tribal region, the main sanctuary for Taliban and al-Qaeda militants in the country.

Much of the funding that was handed to Afghans fighting Soviet rule in neighbouring Afghanistan in the 1980s was channelled through Peshawar. The city's proximity to the tribal region made it a vital place for American officials to be based following the attacks in the U.S. on Sept. 11, 2001, that triggered the invasion of Afghanistan. Many militants have used the tribal region as a base to attack U.S.-led forces in neighboring Afghanistan.