The bomber, who struck the base in Khost Province, was wearing an Afghan National Army uniform, two NATO sources, both of whom asked not to be named because of the sensitivity of the subject, said on Thursday. Earlier, a Taliban spokesman had claimed responsibility for the attack.

The use of an official army uniform could mean any one of the three things: that the raid was carried out by the Taliban, and he was using a stolen uniform; that he was an army officer assigned to the base who became mentally unstable and decided to turn on those he was supposed to protect; or that the Afghan National Army ranks are infiltrated by insurgents. The latter would be the most serious concern because it indicates a potentially more pervasive problem.

The attack at the CIA base, Forward Operating Base Chapman, in Khost Province appeared to be the single deadliest episode for the US spy agency in the eight years since 9/11. It also dealt a significant blow to the often insular, tight-knit organisation, which has lost only 90 officers in the line of duty since its founding in 1947.
A former CIA official said eight agency employees were killed. The official added that the total number of dead could be higher because at least six American civilians were wounded.

The attack occurred as the agency has steadily increased its presence in Afghanistan and Pakistan over the past year, sometimes sending operatives to remote bases instead of to heavily fortified embassies in Kabul and Islamabad.

Drone attacks

In recent years, the CIA has been at the forefront of the American counterterrorism operations in South Asia, launching a steady barrage of drone attacks on Qaeda and Taliban operatives in the mountains along the Afghanistan-Pakistan border. Khost Province, bordering Pakistan, has been a prime area for militants with links to the Taliban and the al-Qaeda who use Pakistan’s lawless tribal areas as a base to stage their insurgency.

There have been frequent attacks on American bases in Khost, but rarely, if ever, do suicide bombers make it past a main gate. Wednesday’s attack was particularly audacious because the bomber managed to breach a secure base assigned to potentially sensitive operations.

A NATO official said the bomber managed to elude security and reach an area near the base’s gym. It was not clear whether the bomber, who apparently died in the blast, entered the gym. Among other questions raised was whether the bomber worked at the base and had clearance, or if a security slip allowed him to gain entry. It is also being examined whether other operatives had access to the base.