Obama said those killed in Khost were 'part of a long line of patriots'
Barack Obama has sent a letter of support to the CIA after seven staff were killed by an Afghan bomber - one of the worst attacks in its history.
The US president's condolence message praised the work of those killed.
The dead include the head of the CIA's base in Khost Province, near the border with Pakistan, the Associated Press news agency reports.
The Taliban said one of their members wearing an explosive vest and an army uniform had carried out the attack.
It was the worst against US intelligence officials since the American embassy in Beirut was bombed in 1983.
A total of 90 CIA employees have been honoured for their deaths in the agency's service since its inception in 1947, according to the Washington Post newspaper.
The bombing has raised questions about the coalition's ability to protect itself against infiltrators, analysts say.
CIA DEATHS: 1965-2009
2009: Seven killed in suicide attack on their 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 the US embassy bombing in Beirut
1965: Seven CIA employees die, most of them in Vietnam
Source: Washington Post
Quoting former CIA officials, AP said the base chief - who was reported to be a mother of three - would have led intelligence-gathering operations in Khost, a hotbed of Taliban activity due to its proximity to Pakistan's lawless tribal region.
An unnamed official added that the bomber was being courted as an informant and was not frisked as he entered Forward Operating Base Chapman.
Paying tribute to the fallen, Mr Obama said those killed were "part of a long line of patriots who have made great sacrifices for their fellow citizens, and for our way of life".
He told CIA employees that they had "taken great risks to protect our country" and that their sacrifices had "sometimes been unknown to your fellow citizens, your friends, and even your families".
CIA Director Leon Panetta said six other agents had been injured in Wednesday's attack.
"Those who fell yesterday were far from home and close to the enemy, doing the hard work that must be done to protect our country from terrorism," he said.
"We owe them our deepest gratitude, and we pledge to them and their families that we will never cease fighting for the cause to which they dedicated their lives - a safer America."
Taliban spokesman Zabiullah Mujahid told the BBC the Khost bomber was wearing an army uniform when he managed to breach security at the base, detonating his explosives belt in the gym.
Neither the names of the CIA officials killed nor the details of their work were released because of the sensitivity of US operations, the agency said.
The flags at the CIA headquarters in Langley, Virginia, are being flown at half-mast in honour of the dead.
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.
In the latest such attack, a US drone fired on a moving car in the Pakistani tribal region of North Waziristan, killing at least three people, Pakistan security officials say. It comes a day after a similar attack in the same area reportedly killed another three suspected militants.