At least four people have been killed and seven wounded after a car bomber attacked a US base in Khost city in eastern Afghanistan, officials say.
Sediq Sediqqi, the Afghan interior ministry spokesman, said on Wednesday the attack was a suicide car bombing and happened near the entrance of Forward Operating Base Chapman in Khost, a Taliban flashpoint that borders Pakistan.
Afghanistan's NATO-led force said the bomber did not get into the base nor breach its perimeter.
"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 blast was so powerful that it rattled the windows of buildings in the city, some four kilometres away, an AFP journalist said.
The attack comes two days after an Afghan policewoman killed a US police adviser at the Kabul police headquarters.
The Taliban, who have waged a bloody guerilla war against foreign and Afghan government forces for the past 11 years since being toppled from power in an invasion led by the US, claimed responsibility for the attack.
"The target was those who serve Americans at that base," Zabihullah Mujahid, Taliban spokesman, said.
"The attack was carried out by a mujahid named Omar from Khost who knew the area very well."
This is the second attack on this base in three years. At least seven CIA agents and his Jordanian handler, were killed in the attack in December 2009 when an al-Qaeda triple agent blew himself up.
Khost, which shares a porous border with Pakistan's tribal belt, is one of the most volatile parts of Afghanistan, and US officials say the Taliban and al-Qaeda have carved out rear bases for operations there.
NATO operates with more than 100,000 troops in the country, including about 66,000 American forces.
It is handing most combat operations over to the Afghans in preparation for a pullout from Afghanistan in 2014.