Amid reported claims from the Afghan Taliban that the group had sent a suicide bomber in a vehicle to attack an American military base, an explosion hit the eastern Afghan city of Khost on Wednesday.
The blast killed at least three Afghans and wounding seven others, officials told AFP news agency.
Afghan interior ministry spokesman Sediq Sediqqi told the agency the attack was a suicide car bombing and happened near the entrance of Camp Chapman base in Khost, close to the border with Pakistan.
"Three Afghan nationals are killed and seven Afghan nationals are wounded. We have no report of coalition casualties right now," Major Martin O'Donnell, a spokesman for NATO's International Security Assistance Force (ISAF), said.
"The attack was carried out by a mujahid named Omar from Khost who knew the area very well," Taliban spokesman Zabihullah Mujahed told AFP.
He said the attacker "detonated a car bomb while American invading forces were searching visitors going to the base."
Khost is one of the most volatile parts of Afghanistan.
It shares a porous border with Pakistan's tribal belt, which lies outside government control, and where U.S. officials say the Taliban and Al-Qaeda have carved out rear bases for operations in Afghanistan.
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.
Earlier this month, a car bomb exploded outside of a compound housing a U.S. military contractor in the Afghan capital, blowing apart an exterior wall and wounding dozens inside, company representatives and police said.
Afghan authorities are scrambling to improve security across Afghanistan before the U.S. combat mission ends in 2014.