BRUSSELS: NATO nations, wracked by budget shortages and engaged in an unpopular war with mounting casualties, will struggle to satisfy the demands of the top commander in Afghanistan for more troops.

In a 66-page assessment of the fight against Taliban-led insurgents, General Stanley McChrystal urges NATO and its partners to boost their military presence and bridge a security gap over the next year until the Afghan army is stronger.

As part of a new strategy, he said in the confidential document leaked to major US newspapers, troops would protect ordinary Afghans and win their confidence rather than focus only on the resilient insurgency.

At the same time, forces have to train Afghan police and the military as planners target a doubling in local security forces from around 134,000 troops and some 80,000 police to more than 400,000 personnel combined.

"His strategy is to occupy more ground, and for that you need more troops," said Francois Heisbourg, at the strategic research foundation in Paris.

But commanders in Afghanistan have repeatedly called for extra forces since NATO took command of the International Security Assistance Force (ISAF) in 2003, and nations have proved slow and reluctant to stump up resources.

"The campaign in Afghanistan has been historically under-resourced and remains so today -- ISAF is operating in a culture of poverty," McChrystal said in his assessment. "Consequently, ISAF requires more forces."

He warned that "inadequate resources will likely result in failure", and said bluntly that if nations forge ahead "without a new strategy, the mission should not be resourced".

ISAF numbers around 65,400 troops drawn from some 40 nations, according to NATO figures from July. A further 40,000 troops are involved in Operation Enduring Freedom, the US-led effort focused on Al-Qaeda.

McChrystal is to send a review of the new requirements at a later date.

At NATO, officials refer to the assessment as a "preliminary" or "draft", raising questions about how much will be taken on board, eight years after the Taliban were forced out of power by a US-led coalition.

NATO spokesman James Appathurai said Monday that the document was "subject to the normal consultations between the capitals of member countries," and that "a military analysis is also being conducted".

He underlined: "We will not be looking at the question of possible reinforcements until this debate has been finalised."

The economic crisis has cut deeply into military budgets and politicians are wary as publics turn against NATO's biggest and most ambitious operation following casualties in major operations in July.

Those missions were launched to prepare for presidential and provincial elections in August, but the polls were tainted by allegations of fraud, undermining local and international support even more.

"We're in a bind," said Heisbourg. "We're perceived as being foreign occupiers but we are incapable of occupation. Things can't go on like this."

"We have to get out of this quagmire and pack our bags, in consultation with neighhbouring countries," he said.

But according to European Union Institute for Security Studies expert Luis Peral, who contributed to the assessment, McChrystal is "conscious that the way the previous strategy was launched and implemented was a big mistake".

The priority now, he said, is "protecting the people".

"The most important part is the qualitative change in strategy. It's closer to the European vision," he said.

But this new approach will hardly have European allies queuing up to send extra troops.

Despite insisting he's an optimist, Peral said: "perhaps it's a little too late to re-engage the Europeans."