A suicide bomber targeted an American base in eastern Afghanistan killing eight civilians, most of them employees of the Central Intelligence Agency, in the deadliest single attack on a US intelligence agency.
The CIA did not either confirm or deny the reports.
The suicide attacker detonated himself on Wednesday at a forward American operating Base Chapman in Khost Province near the Afghan border with Pakistan, an area believed to be controlled by Taliban warlord Jalaludin Haqqani.
The US had recently set up the CIA base in the Khost Province to launch Predator drone attacks targetting the Haqqani network, whose Taliban fighters operate on both sides of Afghan-Pakistan border.
Media reports said an Afghan national was also killed which left six other Americans wounded. The state department spokesman, Ian Kelly, however confirmed the death of eight Americans.
A Congressional source told ABC News that all the dead were connected to CIA. "Eight Americans were killed in an attack on a US military base in Regional Command East in Afghanistan. We mourn the loss of life in this attack, and are withholding further details pending notification of next of kin," Kelly said in a statement.
The Washington Post reported, "The attack represented an audacious blow to intelligence operatives at the vanguard of US counterterrorism operations in both Afghanistan and Pakistan, killing officials whose job involves plotting strikes against the Taliban, al-Qaeda and other extremist groups that are active on the frontier between the two nations."
"It is the nightmare we've been anticipating since we went into Afghanistan and Iraq," John E McLaughlin, a former CIA deputy director who now serves on a board that supports children of CIA officers slain on the job, was quoted as saying by the daily.
"Our people are often out on the front line, without adequate force protection, and they put their lives quite literally in jeopardy," McLaughlin said.
"It was the worst day for the CIA in terms of loss of life since the war in Afghanistan began eight years ago," ABC News said.
The suicide bomber blew himself up in either the gym or the dining facility on Camp Chapman near the Pak border in Khost province, according to one US official in Kabul, the news channel said.
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.
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 US facility, ABC news channel said.
A Taliban spokesman in Afghanistan claimed responsibility for the attack and even went on to claim that 16 Americans had been killed in the strike.