Update: AP reports that bomber was being courted as an informant

A suicide bombing that took the lives of eight Americans in Afghanistan Wednesday was targeted at a CIA base in the eastern part of the country, and represents "the deadliest single attack on US intelligence personnel in the eight-year-long war and one of the deadliest in the agency's history," the Washington Post reported late Wednesday.

A former senior intelligence official has now told the Associated Press that the bomber was invited onto the base without being searched because he was being courted as an informant. An experienced CIA debriefer had come from Kabul specifically for the meeting.

The AP has also learned that one of those killed was the CIA base chief in Afghanistan's Khost Province. This appears to contradict earlier statements from US officials, who told the Post that "most, if not all" of the eight people killed were civilian employees of, or contractors for, the CIA.

The paper described the attack as "an audacious blow to intelligence operatives at the vanguard of US counterterrorism operations in both Afghanistan and Pakistan, killing officials whose job involves plotting strikes against the Taliban, al-Qaeda and other extremist groups."

A suicide bomber managed to penetrate the base's defenses, detonating an explosive belt in a room described as a base gym. Pentagon spokeswoman Lt.-Col. Almarah Belk said the eight Americans died at Forward Operating Base Chapman in Khost province, which is a key Taliban stronghold.

The New York Times said an unidentified NATO official described Chapman as "not a regular base," suggesting it was used by US intelligence agencies.

The attacks come as the number of US and NATO-led foreign troops is set to soar to 150,000 to try to halt an increasingly virulent insurgency by the Taliban militia that has made 2009 the bloodiest year for international forces since the 2001 invasion.

A spokesman for NATO's International Security Assistance Force (ISAF) said that no US or ISAF military personnel were killed or injured in the bombing.

Suicide attacks are a hallmark of the hardline Taliban militia, who are waging a major insurgency to topple the Western-backed government of Afghan President Hamid Karzai and oust the foreign troops.

The United States said last month it had doubled the number of civilian experts working in Afghanistan and was "on track" to meet its goal of nearly 1,000 by the new year. Many are to work in provincial military bases alongside military reconstruction teams.

The latest attacks came as international forces in Afghanistan -- numbering 113,000 and set to grow to 150,000 next year -- are embroiled in controversy over the deaths of Afghan civilians in an operation on Saturday.

In an incident that has inflamed public anger and strained ties between the Kabul administration and the Western military protecting it, President Karzai accused international forces of shooting dead 10 people, most members of the same family and eight of them teenagers.

The incident in eastern Kunar province sparked demonstrations on Wednesday, which saw protesters burning the US flag, shouting "Death to Obama" and calling for foreign troops to leave.

Gen. Stanley McChrystal, the commander of forces in Afghanistan, has reportedly called for an inquiry into the incident.

-- With Agence France-Presse