The victims have not been named in order to protect CIA operations
The suicide bomber who killed seven CIA agents in Afghanistan was an al-Qaeda double agent, US media reports say.
He is said to have been a doctor from Jordan, arrested there a year ago.
He was then reportedly recruited by the Jordanians and CIA, who wrongly thought they had turned him, and given a mission to find al-Qaeda leaders.
The reports came as the top US military intelligence officer in Afghanistan issued a scathing assessment of the state of the intelligence effort there.
In a report, Maj Gen Michael Flynn said that US intelligence in Afghanistan was still "unable to answer fundamental questions about the environment in which US and allied forces operate and the people they are trying to protect and persuade".
The study, published by the think tank Center for a New American Security, cites one officer's remarks that the US was "clueless" due to its lack of useful intelligence about the country.
However the report's findings were rejected by Mike Hurley, a former member of the US 9/11 commission and a former CIA chief in Afghanistan.
He told the BBC: "Nowhere in the report does the group... suggest that there is not a significant role for intelligence to play in finding and fixing and finishing off enemy leaders in Afghanistan. That's precisely their job, that's what they're trying to do."
The attack at Forward Operating Base Chapman was the worst against US intelligence officials since the US embassy in Beirut was bombed in 1983.
The Washington Post quoted two former US government officials as saying that the alleged attacker had lured the CIA officers into a meeting with a promise of new information on al-Qaeda's top leadership.
The reports named him as Humam Khalil Abu-Mulal al-Balawi, a 36-year-old al-Qaeda sympathiser from Zarqa, Jordan, arrested by Jordanian intelligence over a year ago.
CIA DEATHS: 1965-2009
2009: Seven killed in suicide attack on CIA base in Afghanistan
2003: Two CIA contractors die in Shkin, Afghanistan; CIA officer killed during training exercise in Afghanistan
2001: Officer shot during prison uprising in Afghanistan
1993: Two CIA employees killed at the agency's Virginia headquarters
1989: Six CIA employees die when a plane carrying military equipment from DR Congo to Angola crashes
1985: CIA Beirut station chief killed after having been kidnapped and tortured
1983: Eight CIA employees killed in US embassy bombing in Beirut
1965: Seven CIA employees die, most of them in Vietnam
Source: Washington Post
His specific mission was thought to be tracking down al-Qaeda's number two, Ayman al-Zawahiri.
The CIA has declined to comment on the reports.
Jordanian intelligence believed they had brought Humam al-Balawi over to their side and sent him to Afghanistan to infiltrate al-Qaeda, US network NBC says.
According to Western intelligence officials quoted in the reports, Humam al-Balawi called his handlers last week to arrange a meeting at Forward Operating Base Chapman in Khost, where he said he would relay urgent information about Zawahiri.
Once inside the base, the reports say, he blew himself up killing seven CIA employees and his handler, whom Jordanian media have named as Ali bin Zeid.
Questions were raised after the bomb was detonated in the base's gym last week about how the attacker could have managed to pass through security.
The Washington Post says he was picked up in a car outside the base and driven in without being thoroughly searched.
A US official, also a former CIA employee, told the Associated Press news agency that such people were often not required to go through full security checks, in order to help gain their trust.
"When you're trying to build a rapport and literally ask them to risk [their lives] for you, you've got a lot to do to build their trust," he said.
A Taliban spokesman quoted on al-Jazeera's website said Humam al-Balawi was a double agent who had misled Jordanian and US intelligence services for a year.
Forward Operating Base Chapman, a former Soviet military base, is used not only by the CIA but also by provincial reconstruction teams, which include both soldiers and civilians.
The airfield is reportedly used for US drone attacks on suspected militants in neighbouring Pakistan.
The CIA has not released the names of the officials killed nor details of their work because of the sensitivity of US operations.
But the head of the base, reported to be a mother-of-three, was among those killed.
The BBC's Mark Mardell in Washington says the CIA will be deeply embarrassed that the bomber was able to work so closely with the agency and with such high level officials.
Congressman Dutch Ruppersberger, a Democratic member of the House Intelligence Committee, told the BBC it was important to find out why the CIA had not discovered the bomber was an al-Qaeda agent.
He said there was "clearly a breakdown" in security, but added: "I think more and more though when you're dealing with Afghanistan and even Iraq you have double agents and people working both sides."