KABUL (AFP) - With Hamid Karzai confirmed as Afghan president for another five years, the pressure is on Barack Obama to declare his plans for winning a war which commanders say is in danger of being lost.

Top aides have said it would be "irresponsible" for the US president to take a decision on committing tens of thousands more troops to battle the Taliban before it was clear who would be in power in Kabul.

Stanley McChrystal, the US general with overall command of the more than 100,000 troops already in Afghanistan, wants up to 40,000 reinforcements -- a line strongly backed by his senior lieutenants.

But with US and European enthusiasm for the war waning, experts say Obama may opt for a more limited boost in troop numbers. They warn that other options are fraught with difficulties.

In a speech last month, McChrystal warned: "The situation is serious and... neither success nor failure can be taken for granted."

The message was even starker from a commander in the NATO-led security force which provides some two-thirds of the West's troops in Afghanistan.

"The clock is ticking in Afghanistan," the officer said, speaking on condition of anonymity.

"We are losing the support of the population day by day and from a military point of view I am not able to make further progress" with current troop levels.

"If we want to join with the population, live with them in the villages, we have to have more soldiers."

In a new report, the International Crisis Group (ICG), a think tank, warned the Taliban were at their strongest since being overthrown in 2001.

"The insurgents believe that they now have the upper hand," it said.

Many military officers feel a lack of numbers prevents them from keeping rural areas onside.

But other powerful voices such as John Kerry, who heads the US Senate's Foreign Relations Committee, argue that combating terrorism does not require the coalition to "defeat the Taliban in every corner of the country".

Kabul-based analyst Waheed Mujda said the Soviet Union had found piling in soldiers was no guarantee of success. Its army was forced from Afghanistan in 1989, 10 years after invading the country, after being run ragged by mujaheddin rebels.

"History has shown us that more foreign troops is not a solution," said Mujda. "The Soviets, who were our neighbours, deployed 120,000 troops."

In a sign a decision is imminent, leaks have appeared in US media suggesting Obama could opt for a limited increase in troops deployed to big cities.

Mark Schneider, a vice president of the ICG, said Obama could roll out a limited plan which would be ramped up later.

"We could easily see the administration making the judgement that right now we have to send in trainers, mentors at an accelerated pace to train the Afghan military," he said.

Stephen Biddle, part of McChrystal's assessment team that drew up recommendations earlier this year, says putting the emphasis on training would still require many more troops.

"To build an indigenous security force in the middle of a war is not like teaching maths to high school students -- it cannot be done successfully by a handful of teachers in classrooms with chalk and blackboards," he wrote in The New Republic journal.

"This requires Western troops, in large numbers, living and fighting together with Afghan forces at all levels."

Obama himself has hinted at talking to "moderate" Taliban elements and, in his first appearance since his re-election, Karzai proffered an olive branch to his Afghan "brothers".

While Mujda agreed "the solution to the Afghan problem is negotiations with Taliban," Biddle said such an approach was doomed as the Taliban feel they have momentum.

"Taliban leaders appear to believe that they are winning the war," he said.

"This is hardly unreasonable. Why should Taliban leaders compromise for half a loaf when the whole bakery is available?"

In the first couple of years after taking power, Karzai often dismissed the Taliban as a spent force but is now acutely aware of their threat.

Taliban leader Mullah Brader Akhund warned recently that US-led forces would never triumph.

"This war will come to an end when all invaders leave our country and an Islamic government based on the aspirations of our people is formed in the country," he said.