WASHINGTON Most of the eight Americans killed in a suicide attack at a US military base in Afghanistan on Wednesday probably worked for the CIA, which was using the facility, the Washington Post reported.

It said the attack appears to have killed more US intelligence personnel than have died since the US-led invasion of Afghanistan began, the newspaper added.

The agency has acknowledged the deaths of four CIA officers in Afghanistan since the 2001 invasion, according to the Post.

Citing unidentified US officials, the Post said Forward Operating Base Chapman, located in the Afghan province of Khost, was being used in part by the CIA.

A suicide bomber managed to penetrate the bases defences on Wednesday, detonating an explosive belt in a room described as a base gym.

The Post said US sources confirmed that all the dead and injured were civilians, and that most were probably CIA employees or contractors.

The New York Times said an unidentified NATO official described the US military installment as “not a regular base,” suggesting it was used by US intelligence agencies.

There was no public confirmation that the Americans killed in the attack were intelligence personnel, but a spokesman for NATOs International Security Assistance Force (ISAF) confirmed that those killed were civilians.

“No US and no ISAF military personnel were killed or injured,” the spokesman said.