Eight Americans Killed by Afghan Suicide Bomber Were CIA

At least eight Americans were killed and six others injured when a suicide bomber penetrated the heart of a heavily fortified complex in eastern Afghanistan, according to multiple U.S. officials in both Afghanistan and Washington, and and a Congressional source told ABC News they were all connected to the CIA.

The Congressional source could not confirm how many of the dead were CIA staff and how many were contractors, but said the facility was a CIA base. It was the worst day for the CIA in terms of loss of life since the war in Afghanistan began eight years ago.

The suicide bomber blew himself up in either the gym or the dining facility on Camp Chapman near the Pakistani borderin Khost province, according to one U.S. official in Kabul. The same official says all those killed were civilians, and a separate official in Washington said the base is not used by State Department employees -- suggesting the victims may be intelligence officials.

VIDEO: Eight U.S. Civilians Killed by Afghan Suicide BomberPlay

The attack appears to have been the result of an extraordinary lapse in security, one of the few times that any militant has managed to elude guards and attack inside a U.S. facility.

The area of the attack is near a Taliban stronghold where insurgents who use Pakistan as a base flow easily back and forth across the border. Militants in the area are led by the Haqqani family, whom U.S. officials say is responsible more than any other insurgent leader for attacks on U.S. soldiers.

Khost has suffered from multiple attacks, including suicide bombings near the main U.S. military camp called Solerno. In May and June, attacks in Khost City or outside Solerno killed at least 21 civilians, most of them Afghan day laborers.

But today's attack was directed at a non-military camp and appears to be the deadliest against American civilians since the start of the war. In August, 16 civilians died in a helicopter crash in Kandahar, but that was due to mechanical failure.

U.S. officials declined to provide any more specifics about the people who were killed today, saying the next of kin were still being notified.

The attack comes on the same day the U.S. military defended itself after hundreds of Afghans protested a weekend raid that Afghan government officials say killed 10 Afghan civilians.

The incident, which took place in the Narang district of Kunar Province, occurred on Saturday night when a group of U.S. and Afghan soldiers entered a small village called Ghazi Khan.

According to the U.S. military, the troops came under fire "from several buildings" and killed nine insurgents. But an Afghan commission led by an advisor to President Hamid Karzai concluded the troops "descended from a plane... took 10 people from three homes, eight of them school students in grades six, nine and ten, one of them a guest, the rest from the same family, and shot them dead."

U.S. Military Denies Latest Accusation of Civilian Deaths in Afghanistan

The NATO-led military forces in Afghanistan denied that, saying in a statement released today that "there is no direct evidence to substantiate these claims." But the statement went on to welcome a joint investigation by both Afghan and military officials, and said if any operation kills civilians, "we will always look within to improve our capacity to avert unintended consequences in the future."

That tone is an acknowledgement that civilian casualties is probably the single most sensitive issue in Afghanistan. It has helped sour relations between Karzai and the United States, and U.S. officials admit high profile civilian casualty incidents have pushed some Afghans -- often family members of victims – toward the Taliban.

Many Afghans acknowledge that the U.S. has reduced the number of civilian casualties in 2009, and Afghan politicians praised U.S. commander Gen. Stanley McChrystal for the positive change during a meeting last month.

According to U.S. statistics, 225 Afghan civilians have been killed or injured in military actions in 2009, not including an air strike in northern Afghanistan in September that Afghan officials say killed as many as 100 civilians. In 2008, 407 Afghan civilians were killed or injured in military actions.

But that progress did not stop hundreds of people from protesting the Kunar raid.

"We have no more patience. It has happened repeatedly. If it occurs again, we will drop our pens and take arms," one group of protestors chanted in the eastern city of Jalalabad, according to Reuters. "Death to Obama. Down with Karzai."

In Kabul, young men carried a sign that said "Obama! Take your soldiers out of Afghanistan!" One group of protestors displayed pictures of young children they said had been killed by foreign troops. "Death to the enemy of Islam!" screamed a protester with a bullhorn.