Police said a suicide car bomber attacked the heavily fortified Afghan capital, killing at least three people.
Police said that initial reports of the explosion today in the west of Kabul indicated that US vehicles were targeted.
The area around the blast site is also home to Afghan government buildings.
A reporter on the scene saw the wreckage of a public bus and four smaller vehicles. It was not immediately clear what type of vehicles they were.
US soldiers and Afghan police were working to secure the site as news trickled out of deaths and injuries.
A police officer at the scene, Habibullah Mohammadi, said he saw three dead bodies. A doctor said at least 12 wounded people were evacuated to hospitals.