Two Americans working for the U.S. consulate were wounded on Monday in a bomb attack on their vehicle in the Pakistani city of Peshawar, the American embassy said.
The blast also wounded two Pakistani employees of the consulate, the embassy in Islamabad said in a statement.
Earlier, regional Information Minister Mian Iftikhar Hussain told reporters at least four people, including two Americans, were killed in an attack by a suicide bomber in a vehicle.
"We can confirm that a vehicle belonging to the U.S. consulate in Peshawar was hit in an apparent terrorist attack," the U.S. embassy said in its statement.
"Two U.S. personnel and two Pakistani staff of the Consulate were injured and are receiving medical treatment."
There was no immediate claim of responsibility for the blast, which left a crater in a busy street. Firemen could be seen putting out a vehicle that was mangled and blackened from the explosion.
Television stations repeatedly broadcast an image of a U.S. passport at the scene, its corners scorched by fire.
U.S. Secretary of State Hillary Clinton condemned the attack.
"Once again we deplore the cowardly act of suicide bombing and terrorism that has affected so many people around the world and which we all must stand against," she told reporters on a visit to Indonesia.
Pakistan's Taliban, who are close to al Qaeda, are blamed for many of the suicide bombings across Pakistan, a strategic U.S. ally.
Those attacks had eased in recent months but it was not clear if the lull was due to pressure from military offensives or a shift in tactics.
Peshawar is an old trading city on the main route into nearby Afghanistan. It has been plagued by militant attacks for years.