A blast in the eastern Afghan city of Khost on Wednesday wounded three people, and the Taliban said they had sent a suicide bomber in a vehicle to attack an American military base.
The area's police chief said the explosion took place near a U.S. base, which is beside a military airport. Hospital officials said three people were wounded and the number of casualties was expected to rise.
The al Qaeda-linked Haqqani network, widely regarded as the United States' most dangerous foe in Afghanistan, is active in Khost, which is on the Pakistani border.
Three years ago, an al Qaeda-linked Jordanian double-agent killed seven CIA employees and a Jordanian intelligence officer in a suicide bombing at a U.S. base in Khost.
Afghan authorities are scrambling to improve security across Afghanistan before the U.S. combat mission ends in 2014.