Afghanistan's long years of unrest have produced a new generation of Islamic militants, many of them bent on holy war, who are reinforcing the "old Taliban" in their deadly insurgency, analysts say.
When the Taliban regime was toppled in a US-led invasion in late 2001, the hardliners were considered a spent force.
But in their safe havens across the border in Pakistan, they have been able to regroup, recruit and — armed with new ideologies, funds and warfare from the Al-Qaeda terror network — make a deadly comeback, analysts say.
"Today's Taliban are different to what they were in 2001," said Waheed Mujda, a former foreign ministry official in the Taliban government who has written a book on the hardliners' five years in office.
"Back in 2001 and before, the Taliban were a nationalist movement trying to gain power and bring stability to Afghanistan," he said, referring to the anarchy of the 1990s when the country was mired in civil war.
"Over the past seven or eight years, most of their leaders have turned into dangerous radical Islamists who now think beyond Afghanistan's borders, willing to confront US interests worldwide — something like Al-Qaeda."
The presence of thousands of (mainly Western) foreign troops in Afghanistan has helped these leaders recruit a new generation of fighters to battle what they call "the occupation of their Islamic land by infidels," he said.
"There are some Arab fighters among them, maybe hundreds, and some Pakistani jihadists, but most of the fighters are ordinary Afghans — youths recruited from remote villages and refugee camps in Pakistan," Mujda said.
"In Afghanistan it's never difficult to find fighters for wars against foreign elements, especially if they are non-Muslims," he said.
Afghan historian and political commentator Habibullah Rafi agreed.
The insurgents fighting against the US-backed government of President Hamid Karzai are a "combination of old and new Taliban," he said.
"The leaders are the same old leaders but the foot soldiers are new recruits who have joined the Taliban against the international forces in a holy war.
"The Taliban message is, 'Defend your country against foreign occupation'. This is a strong message, which has helped recruit thousands of new fighters from among passionate Afghan villagers."
Afghanistan's mostly destitute villages have perhaps seen the least of the billions of dollars in foreign aid that have been pumped into the country since the fall of the Taliban government.
The jobs, development and assertion of authority by Karzai's government and security forces have not reached the villages, creating a disaffected pool of uneducated young men hungry for cash and power — ripe for Taliban recruitment.
"The absence of Afghan forces in the provinces has created a favourable situation for the Taliban," analyst Haroon Mir from the Afghanistan Centre for Research and Policy Studies said.
"Taliban take advantage of the population's dissatisfaction with the government and with the foreign presence in the country," he said.
The international military forces here describe tiers of men involved in the unrest — from hard-core ideologues influenced by Al-Qaeda, to "guns for hire," to those who want instability so the illegal opium trade remains unchecked.
This makes it difficult to say how many Taliban fighters there actually are, but US military officials have said they may number up to 20,000.
The military says it has been able to take out some mid-level commanders in the Taliban's "old guard" although the movement's fugitive leader, the one-eyed Mullah Mohammad Omar, is still at large.
This has seen the emergence of "less ideological individuals less concerned about using un-Islamic methods of warfare and of raising funds," said British Lieutenant General Jim Dutton, deputy commander of the NATO-led force, referring to suicide attacks and the opium business.
"There is no doubt that Al-Qaeda is providing financing, it is providing command and control," he added.
"It's helping recruiting, logistics, intelligence and training from across the border in the safe areas, in the tribal areas of Pakistan."
Closely linked to the Taliban is the Haqqani network, led by Jalaluddin Haqqani, which is suspected of staging some of last year's most spectacular attacks in Kabul, such as the storming of a five-star hotel.
The other main radical Islamic group active here is Hezb-e-Islami of former prime minister Gulbuddin Hekmatyar which carries out attacks mainly in the east and near Kabul, apparently separate from the Taliban.
But "Taliban are still the main group behind this insurgency," Mujda said.
Taliban spokesman Yousuf Ahmadi, asked about claims that his fighters are trained in Pakistani camps funded by Al-Qaeda and foreign Islamist groups, responded: "We are Afghans."
"Taliban are not the product of a factory," Ahmadi told AFP by telephone. "They have risen from this society and are being supported by this society. We are fighting for our beliefs."