The U.S. Embassy in Pakistan says two Americans working for the U.S. Consulate in the northwestern city of Peshawar were wounded in a bomb attack that targeted their vehicle.
A U.S. Embassy statement said the September 3 attack near the Afghan border had also injured two Pakistani employees of the Peshawar Consulate.
The statement said that "an apparent terrorist attack" had targeted a U.S. vehicle, and that two Americans and two Pakistanis had been injured and were receiving medical treatment.
Earlier, Pakistani officials had said at least three people -- including two Americans -- had been killed in a suicide car-bombing attack on their vehicle.
The conflicting reports could not immediately be reconciled.
Nineteen people were reported injured in the blast.
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U.S. State Department spokeswoman Victoria Nuland said in a statement that Washington "stands ready to work with Pakistani authorities on a full investigation so that the perpetrators can be brought to justice."
The blast occurred in a high-security area of Peshawar where foreign organizations, including the U.S. Consulate and a United Nations office, are located.
"The blast took place at 9:05 a.m. When I came out, I saw a vehicle [that was driven by] foreigners," said Hazrat Ali, a security guard and witness to the bombing.
"One foreigner was burning in flames and another one, who was injured, threw himself out [of the car]."
An unidentified doctor in a nearby hospital said: "We received 21 patients. Of those, two are dead and 19 are injured. They also include women and children. Eighty percent of the injured are in serious condition."
Senior police officer Javed Khan said a U.S. passport was found in the wreckage of the vehicle that was attacked.
Local TV footage showed an sports utility vehicle at the site that was completely destroyed and burned.
All that was left was a carcass of blackened, twisted metal. The images, officials said, were of the U.S. vehicle that was attacked.
The vehicle was reportedly attacked after it left the U.S. Consulate.
It was not immediately clear who was responsible for the bombing. The Pakistani Taliban have been blamed for previous similar attacks.
Mian Iftikhar Hussain, information minister for Khyber Pakhtunkhwa Province, told the AFP news agency, "This is a dangerous move from the terrorists -- they want to terrorize the foreigners."
Peshawar is located near Pakistan's semiautonomous tribal region, the main sanctuary for Taliban and Al-Qaeda militants in the country.
The city has been hit by scores of bombings in recent years, but attacks against U.S. targets are considered relatively rare because of the extensive security measures taken by the U.S. government.
With reporting by Reuters, AP, and RFE/RL's Radio Mashaal