The attack was a blow to the CIA, which has lost only four operatives in this country since the Sept. 11, 2001 terrorist attacks. It also was the deadliest for Americans since eight soldiers were killed Oct. 3 when insurgents attacked a remote base, also in eastern Afghanistan.
Among those killed was the chief of the CIA's operation at Camp Chapman in the Khost province of eastern Afghanistan, The Associated Press has learned. Former CIA officials said the base chief, a mother of three, would have directed and coordinated CIA operations and intelligence gathering in the province, a hotbed of Taliban and insurgent activity because of its proximity to Pakistan's lawless tribal region.
"There's still a lot to be learned about what happened," said CIA spokesman George Little. "The key lesson is that counterterrorism work is dangerous. Our fallen and wounded colleagues were on the front lines, conducting essential operations to protect our country."
A U.S. intelligence official said the attack will be avenged through successful, aggressive counterterrorism operations, and said the climate at CIA's headquarters in Langley, Va. is "determined."
Earlier, a U.S. official who was briefed on the blast said eight U.S. civilians and an Afghan were killed.
Harold E. Brown Jr., of Fairfax, Va., was among the dead, according to his father, Harold E. Brown Sr. The elder Brown said Thursday that his 37-year-old son, who grew up in Bolton, Mass., served in the Army and worked for the State Department. He is survived by a wife and three children ages 12, 10 and 2.
The attack, which wounded six according to Panetta, came on a bloody day for NATO forces. A roadside bombing, also claimed by the Taliban, killed four Canadian troops and a Canadian journalist in southern Afghanistan. Elsewhere, police said militants beheaded six Afghans on Thursday for cooperating with government authorities; it was unclear whether there was any connection between the beheadings and the infiltration of the CIA post.
Also Thursday, the United Nations said a preliminary investigation showed that a raid last weekend by foreign troops in a tense eastern Afghan province killed eight students. The attack sparked protests by Afghans against foreign troops. Meanwhile, France's Foreign Ministry said two French journalists and their local guides were missing in Afghanistan.
It was unclear how the suicide bomber was able to circumvent security at the U.S. base.
Taliban spokesman Zabiullah Mujahid said in a statement that an Afghan National Army officer wearing a suicide vest entered the base and blew himself up inside the gym. The U.S. official said it took place in the gym.
There was no independent confirmation that the bomber in the attack on the U.S. base was a member of the Afghan military. Gen. Mohammad Zahir Azimi, spokesman for the Afghan Ministry of Defense, said no Afghan National Army soldiers are at the base.
But an Afghan official in Khost said the U.S. has hired about 200 Afghans to help with security at the base. They are usually deployed on the outer ring of its walls, although some work inside, the official said on condition of anonymity because of the sensitivity of the issue.
"It's not the first time that Afghan forces have conducted such an attack to kill Americans or foreigners," the Taliban statement said, citing the alleged killing of an American soldier and the wounding of two Italians this week in Badghis province. NATO has provided no details of that incident, but Afghan Gen. Jalander Shah Bahnam said an Afghan soldier opened fire on a base in the province's Bala Murghab district.
An online message posted by the Afghan Taliban said 20 CIA staff were killed and 25 other people were wounded, according to SITE Intelligence Group, a U.S.-based terrorist tracking organization.
The Taliban routinely exaggerate claims of enemy casualties.
Afghan officials said no members of the Afghan National Army or Afghan National Police worked at the base.
Only four known CIA operatives had been killed in Afghanistan since the Sept. 11, 2001 terrorist attacks. CIA officer Micheal "Mike" Spann was killed in a prison uprising in November 2001. An agency officer died in a training exercise in 2003, and two contractors operating out of a CIA base in Shkin district of Paktika province were killed the same year.
Forward Operating Base Chapman used to be a military base, but was later turned into a CIA base, according to a U.S. official. Some military men and women work there on a Provincial Reconstruction Team, one of several joint civilian-military units that secure and develop areas of Afghanistan. A NATO spokesman said "other personnel" operate from Chapman as well, but he said he could not elaborate.
All the U.S. officials and former CIA officials spoke on condition of anonymity because they were not authorized to discuss the matter publicly.
Chapman is not the only U.S. base in Khost city. Also there is a major U.S. military base known as Camp Salerno, which includes a large Soviet-built airfield.
Camp Salerno and its outlying fire bases have been the focus of repeated militant suicide, artillery and sniper attacks over the past several years. One of the most brazen of the war occurred in August 2008 when a group of about 100 Taliban fighters broke through the perimeter of the base, which houses about 2,000 allied troops. After a two-hour firefight, the guerrillas were forced to retreat by attacking helicopter gunships.
In Wednesday's other attack, NATO said the four Canadian troops and the reporter embedded in their unit died when their armored vehicle hit a bomb while on an afternoon patrol south of Kandahar city.
Michelle Lang, a 34-year-old health reporter with the Calgary Herald, was the first Canadian journalist to die in Afghanistan. She arrived in the country just two weeks ago. Lang "was one of those journalists who always wanted to get to the bottom of every story so this was an important trip for her," said a Calgary Herald colleague, Colette Derworiz.
The military has not disclosed the names of the Canadian troops because relatives have not all been notified.
Brig. Gen. Daniel Menard, commander of coalition forces in Kandahar, said the soldiers were conducting a community security patrol.
According to figures compiled by The Associated Press, 32 Canadian troops have been killed in Afghanistan this year; in all, 138 have died in the war.
Associated Press writers Deb Riechmann, Jim Heintz and Dusan Stojanovic in Kabul; Matthew Lee, Pam Hess and Pauline Jelinek in Washington; and Adam Goldman in New York City contributed to this report.