With the end of the US surge in Afghanistan, the Taliban have survived the biggest military onslaught the West will throw at them -- and fears are growing that a disastrous new civil war looms.

The last of the extra 33,000 soldiers President Barack Obama deployed nearly three years ago left late last month, and the remaining NATO force of some 112,000 will follow by the end of 2014.

Although a small contingent of foreign troops may remain to conduct counter-terror operations, Western politicians stress that what Obama once called the "good war" will "end" in 2014.

But while the unpopular conflict might end for NATO, some analysts predict a collapse of the Western-backed government and a civil war worse than that in the 1990s when Soviet troops withdrew after their own 10-year occupation.

"I think it is only a matter of time before the government collapses. That is certain," says Candace Rondeaux of the International Crisis Group.

"What will come to dominate in Kabul in 2014, 2015 will be chaos and violence.

"And the fracturing that we saw in the 1990s will only be compounded by the fact that there are more weapons in the country and greater incentives now for a lot more brutality than we have seen before."

Afghan expert Gilles Dorronsoro of the Carnegie Endowment for International Peace also predicts renewed strife, but goes further to foresee a Taliban return to power.

"After 2014, the level of US support for the Afghan regime will be limited and, after a new phase in the civil war, a Taliban victory will likely follow," he wrote in a recent analysis.

This contrasts sharply with forecasts by the NATO military and Western governments that Afghan forces will be able to defend the country after 2014.

That claim is "completely unrealistic", Rondeaux says, noting that the often illiterate and poorly trained troops "have no air resources, zero logistical supply capability and zero real cohesion".

The Taliban have also proved adept at tactics: if they lost territory in the south, they assassinated key officials, staged high-profile attacks that humiliated their enemies and infiltrated the Afghan security forces.

Last month, for example, they stormed onto one of the largest NATO bases in the country, destroying six fighter aircraft in the biggest single loss of air assets for the United States since the Vietnam War.

One of the aims of the surge was to put so much pressure on the Taliban that they would come to the negotiating table, but the insurgents called off early contacts in March, accusing the United States of constantly changing its position.

The New York Times reported this week that US generals and civilian officials have now all but written off the prospect of a Taliban peace deal.

Afghan Foreign Minister Zalmai Rassoul told Washington on Wednesday that the government would still work "vigorously" to seek peace with the Taliban, but the Islamists have always refused direct talks with what they call a "puppet" regime.

Secretary of State Hillary Clinton pledged after meeting Rassoul that the United States would stand by Afghanistan "despite the challenges".

The surge also never managed to cut off support in Pakistan for insurgent groups, which Rondeaux said meant "nothing has shifted strategically".

Pakistan, where more Pakistani soldiers have died at the hands of a local Taliban insurgency than US troops have been killed in Afghanistan, is widely accused of continuing to support the Afghan Taliban, who have havens on Pakistani soil.

But in Islamabad, there are fears that the US withdrawal will increase the spillover of civil strife into Pakistan, says political analyst Hasan Askari.

"The Taliban may not succeed completely in overthrowing the government in Kabul, but they can make life miserable and in certain areas... the Afghan government will have limited control," he told AFP.

Although Pakistan was an ardent supporter of the 1996-2001 Taliban regime, its relationship since with the hardline faction has been uneasy at best.

"Terrorism will continue, so I think it's a mixed package for Pakistan and personally I don't see Pakistan in a position to manage these kind of groups that are based in Pakistan or stop the movement across the border," said Askari.

In Afghanistan, the United States has also seen its image tarnished among ordinary Afghans this year by the burning of Korans at a military base, the abuse of corpses and a massacre of civilians by a rogue soldier.

An unprecedented number of Afghan security personnel have turned their weapons against their allies, killing at least 51 NATO soldiers this year.

Despite this, many Afghans, particularly in the cities, fear the departure of the Western troops in a country where the government of President Hamid Karzai is widely seen as corrupt and dependent on foreign support.

"Many, many Afghans are preparing for their exit from Kabul and contingency plans are already under way at a very personal level," says Rondeaux.

Dorronsoro said the withdrawal of international forces will in some respects leave the country worse off than it was before the 2001 invasion, which ousted the Taliban for harbouring Al-Qaeda leader Osama bin Laden.

"In the end the withdrawal is the result of a failed strategy," he wrote.

The US administration denies this, but there was no fanfare at the end of the surge and the war has become so unpopular that both Obama and his rival for the presidency, Mitt Romney, barely mention it.