AFP, Kabul

Eight Americans possibly working for the CIA were killed when a suicide bomber blew himself up after sneaking into the gym on a US base in Afghanistan on Wednesday, officials and US media reports said.

The Taliban said Thursday it was behind bombings that killed eight Americans reportedly working for the CIA and five Canadians in one of the deadliest bouts of violence against Westerners in Afghanistan.

"We claim responsibility for the attack," purported Taliban spokesman Zabiullah Mujahid told AFP by telephone from an undisclosed location.

Four Canadian soldiers and a woman journalist were also killed when a bomb exploded as their armoured vehicle passed by on Tuesday, in one of the deadliest 24 hours for foreigners in the war-torn country.

The attacks come as the number of US

and Nato-led foreign troops is set to soar to 150,000 to try to halt an increasingly virulent insurgency by the Taliban militia that has made 2009 the bloodiest year for international forces since the 2001 invasion.

Pentagon spokeswoman Lt Col Almarah Belk said the eight Americans died when an attacker detonated a vest packed with explosives on Forward Operating Base Chapman in Khost province — a key Taliban stronghold.

"Eight Americans have been killed in an attack on RC-East,” a US embassy official said, using the military term for a region of eastern Afghanistan.

A spokesman for Nato's International Security Assistance Force (Isaf) said that no US or Isaf military personnel were killed or injured in the bombing.

But the Washington Post newspaper said that most of the eight probably worked for the CIA, which it said was using the Chapman base.

A suicide bomber managed to pene-

trate the base's defences, detonating an explosive belt in a room described as a base gym.

The Post said US sources confirmed that all the dead and injured were civilians, and that most were probably CIA employees or contractors.

It said the attack appears to have killed more US intelligence personnel than have died since the US-led invasion in 2001, adding that the agency has acknowledged the deaths of four CIA officers in Afghanistan since then.

Suicide attacks are a hallmark of the hardline Taliban militia, who are waging a major insurgency to topple the Western-backed government of Afghan President Hamid Karzai and oust the foreign troops.

The United States said last month it had doubled the number of civilian experts working in Afghanistan and was "on track" to meet its goal of nearly 1,000 by the new year. Many are to work in provincial military bases alongside militaryreconstruction teams.