(RFE/RL) -- Security has been tightened in the Afghan city of Khost after a suicide bomber killed seven CIA officers and an Afghan man inside a base in the city on December 30.
It was the second-deadliest attack in the agency's history, after a bombing at the U.S. Embassy in Beirut in 1983.
In Washington, the CIA promised to avenge the blast. Reuters quotes an unnamed U.S. intelligence official as saying, "This attack will be avenged through successful, aggressive counterterrorism operations."
The bombing took place in Forward Operating Base Chapman, near the border with Pakistan, where the CIA has been at the forefront of a mounting battle against Islamist extremists. The base -- a former Soviet outpost now also used by military and civilian reconstruction teams -- is reported to have been central in the organization of attacks by unmanned drone aircraft on suspected militants in Afghanistan and Pakistan.
Among those killed was the head of the CIA base. Two of the dead were contractors from private security company Xe, formerly known as Blackwater
, CNN reported.
The Taliban said the attack was carried out by a sympathizer in the Afghan Army who detonated a vest of explosives at a meeting with CIA workers. The Afghan Defense Ministry denied any Afghan soldiers were involved or stationed at the base. Six CIA employees were wounded in the blast.
U.S. President Barack Obama praised the CIA in a written statement.
"These brave Americans were part of a long line of patriots who have made great sacrifices for their fellow citizens, and for our way of life," he said.
CIA Director Leon Panetta said the attack would not deter the agency, saying "those who fell…were far from home and close to the enemy, doing the hard work that must be done to protect our country from terrorism."
The CIA is probing security at the Khost base amid questions over how a suicide bomber was able to enter its heavily fortified premises.
Also on December 30, five Canadians -- four soldiers and a journalist -- were killed when their armored vehicle was hit by a bomb in southern Kandahar Province.
Violence in Afghanistan has reached its highest level since the overthrow of the Taliban regime by a U.S.-led invasion in 2001.
The CIA has been expanding its operations in Afghanistan, stepping up strikes against Taliban and Al-Qaeda militants along the border with Pakistan.
In the latest attack, a U.S. missile strike
killed three people near the Afghan border today, according to Pakistani security officials. Officials say the attack destroyed a car carrying three men in North Waziristan. A U.S. drone missile strike late on December 31 in the same area also killed three people.