An explosives-filled car slammed into a U.S. Consulate vehicle in the Pakistani city of Peshawar on Monday, authorities said.
There was confusion about the extent and severity of injuries as a result of the blast.
Victoria Nuland, a spokeswoman for the U.S. State Department, said "two U.S. personnel and two Pakistani staff of the Consulate were injured and are receiving medical treatment." No U.S. consular employees were killed, she said.
She said U.S. authorities were "seeking further information about other victims of this heinous act."
Nuland's statement followed an assertion by local Information Minister Iftikhar Hussain that two Americans had died in the blast.
Pakistani police and health officials said two Pakistanis were killed and 25 people were wounded.
Umar Riaz, a senior Peshawar police official, said the U.S. consular security detail surrounded the vehicle, which was severely damaged, and took away the people who'd been traveling in it.
As a result, Riaz said, he had no information about the people who were in the consular vehicle.
U.S. Secretary of State Hillary Clinton said the bomber was apparently targeting a U.S. Consulate van filled with both Americans and Pakistanis.
"Let me just very clearly condemn the attack on our consulate personnel in Peshawar, Pakistan. We pray for the safe recovery of both American and Pakistani victims and once again we deplore the cowardly act of suicide bombing and terrorism," she said.
Clinton praised the response of Pakistani authorities, saying some of the injured were airlifted to hospitals in Islamabad.
The attack took place in an area of the city where several international agencies have offices. In addition to the U.S. Consulate, the U.N. refugee agency, UNHCR, is in the area.
Peshawar is about 190 kilometers (120 miles) from the country's capital, Islamabad.
In May 2011, a remote-controlled car bomb targeted a convoy of U.S. Consulate vehicles in Peshawar, killing one person and wounding 11. The Taliban claimed responsibility for the attack.
In April 2010, three explosions went off in rapid succession near the consulate.
Khyber Pakhtunkhwa province, of which Peshawar is the capital, is rife with Islamic extremists and has been the site of recent clashes between Pakistani security forces and militants.
It was formerly known as North West Frontier province, a name assigned during British colonial rule. The ruling party changed the name to reflect the province's majority Pashtun population.