The Taliban said it was behind bombings that killed seven CIA officers and separately five Canadians in one of the deadliest bouts of violence against Westerners in Afghanistan.

The Afghan government also demanded that it be given custody of foreigners wanted over the alleged killing of 10 civilians, sharply escalating a war of words with its Western military backers at a time of increased insecurity.

The seven CIA officers were killed and six wounded in a suicide attack on a US base in eastern Afghanistan, the Central Intelligence Agency confirmed on Thursday.

The five Canadians, including a woman journalist, were killed in a separate militant attack, also this week.

It also emerged Thursday that two French journalists had been kidnapped by suspected Taliban militants in eastern Afghanistan.

The incidents come as the number of US and Nato-led foreign troops is set to soar to 150,000 in a bid to halt an increasingly virulent insurgency that has made 2009 the bloodiest year for international forces since the invasion.

The CIA issued the confirmation after media reports said as many as eight CIA employees were killed in the attack Wednesday, in which a Taliban bomber managed to penetrate the defences of a base in the province of Khost, detonating an explosives belt in a room described as a gym.

US President Barack Obama sent a letter to CIA employees, offering condolences for their colleagues' deaths.

"The men and women who gave their lives in Afghanistan did their duty with courage, honor and excellence, and we must draw strength from the example of their sacrifice," Obama said.

Purported Taliban spokesman Zabiullah Mujahid said by telephone from an undisclosed location said the Taliban took "responsibility for the attack."

"Yesterday evening on a base near the old airport in Khost city a suicide bomber by the name of Samiullah committed a suicide attack by detonating his vest and killed 16 Americans," said Mujahid.

Deadly roadside bomb

The Taliban routinely exaggerate the impact of their operations.

The base had been used by the CIA and one of the many provincial reconstruction teams that dot the country. The teams are tasked with delivering humanitarian assistance and stabilising difficult areas.

Afghan defence ministry spokesman Zahir Azimi said Taliban claims that the suicide bomber was an army officer were baseless.

Taliban militants also claimed responsibility for the deaths Tuesday of four Canadian soldiers and a journalist killed when a roadside bomb exploded under an armoured vehicle in the southern militant stronghold of Kandahar.

Afghan President Hamid Karzai "strongly condemned the terrorist attacks that killed foreign civilian and military personnel in the provinces of Khost and Kandahar."

But Afghanistan's powerful National Security Council, chaired by Karzai, called for action after Afghan government investigators accused Western forces of killing civilians.

Karzai has been vocal in condemning international forces he believes are responsible for an incident last Saturday in Kunar, in which 10 civilians, eight of them teenagers, were shot dead.

NATO has disputed the accusations, saying the foreigners involved were non-military Americans on a sanctioned operation who fired in self-defence after being shot.

Suspected Taliban, meanwhile, have kidnapped two French journalists working for France's public television broadcaster and three Afghan companions.

Gunmen snatched the group as they were travelling around 60 kilometres from the Afghan capital on Wednesday, a French journalist working with them told AFP.

In the south, Afghan authorities said they were also investigating reports of civilian deaths in a NATO air strike in Helmand province.

The probe was launched after reports that nine civilians were killed in the air strike near the town of Lashkar Gah.

Police in neighbouring Uruzgan province said six men were beheaded as "spies" by Taliban militants while one man survived with a massive gash across his throat.