The announcement was nearly impossible to verify independently because it involves covert operations in a dangerous region. It is highly unusual for the Pakistani Taliban to claim credit for an attack in Afghanistan, and the proclamation followed indications the Afghan Taliban may have been involved in the attack.
CIA spokesman George Little could not confirm the account.
"There is much about the attack that isn't yet known, but this much is clear: The CIA's resolve to pursue aggressive counterterrorism operations is greater than ever," he told The Associated Press.
The suicide bomber struck the CIA's operation at Camp Chapman in eastern Khost province on Wednesday. The base was used to direct and coordinate CIA operations and intelligence gathering in Khost, a hotbed of insurgent activity because of its proximity to Pakistan's lawless tribal areas, former CIA officials said. Among the seven killed was the chief of the operation, they said.
Six other people were wounded in what was one of the worst attacks in CIA history.
Qari Hussain, a top militant commander with the Pakistani Taliban who is believed to be a suicide bombing mastermind, said militants had been searching for a way to damage the CIA's ability to launch missile strikes on the Pakistani side of the border.
Using remote-controlled aircraft, the U.S. has launched scores of such missile attacks in the tribal regions over the past year and a half, aiming for high-value al Qaeda and other militant targets.
The most successful strike, in August, killed former Pakistani Taliban chief Baitullah Mehsud at his father-in-law's home. The latest strike, on Friday, killed three suspected militants in a car.
The Washington Post reported Friday that the CIA base has been at the heart of overseeing this covert program. The newspaper cited two former intelligence officials who have visited Chapman as saying that U.S. personnel there are heavily involved in the selection of al Qaeda and Taliban targets for the drone aircraft strikes.
Hussain said a "CIA agent" contacted Pakistani Taliban commanders and said he'd been trained by the agency to take on militants but that he was willing to attack the U.S. intelligence operation on the militants' behalf. He did not specify the nationality of the "agent."
"Thank God that we then trained him and sent him to the Khost air base. The one who was their own man, he succeeded in getting his target," Hussain told an AP reporter who traveled to see him in South Waziristan on Friday. The region is where Pakistan's army is waging a military offensive aimed at dismantling the Pakistani Taliban.
Two former U.S. officials told the AP that the bomber had been invited onto the base and not searched. One official, a former senior intelligence employee, said the man was being courted as an informant and that it was the first time he had been brought inside the camp.
The Pakistani army's offensive in South Waziristan is believed to have forced many Pakistani Taliban leaders to go on the run to other parts of the tribal belt. The group's recent claims that it has sent most of its fighters to help its brethren in Afghanistan were met with skepticism by analysts who said it is trying to worsen the already tense relationship between the U.S. and Pakistan.
Ishtiaq Ahmad, a professor of international relations at Quaid-i-Azam University in Islamabad, said the Taliban's latest claim was likely untrue and just another attempt at driving a wedge between the allies because of the military campaign.
"Since the Pakistan army is succeeding, they are trying to complicate Pakistan-U.S. relations," he said. "It only reflects increasing depression."
After Wednesday's attack, Afghan Taliban spokesman Zabiullah Mujahid said an Afghan National Army officer wearing a suicide vest had entered the base and blew himself up. There has been no independent confirmation of the bomber's identity. It was unclear if the Afghan Taliban statement was a claim of responsibility or simply an accounting of what the militants alleged happened.
The Pakistani Taliban and the Afghan Taliban are separate, though linked, insurgent movements. The Afghan Taliban are focused on ridding Afghanistan of Western troops and toppling the U.S.-backed government in Kabul, while the Pakistani Taliban are primarily determined to overthrow the U.S.-allied government in Islamabad.
Both militant movements are largely driven by Pashtuns, an ethnic group that straddles both sides of the Afghan-Pakistan border and whose members easily slip back and forth between the countries.
In Washington, CIA director Leon Panetta said Thursday that the seven killed in the Khost attack "were far from home and close to the enemy, doing the hard work that must be done to protect our country from terrorism."
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, Virginia, is "determined."
By Associated Press Writer Rasool Dawar