By Jonathan Marcus
Diplomatic correspondent, BBC News
British troops are said to be bearing the brunt of the mission
"We're fighting a war in southern Afghanistan. This is not an enhanced peace support operation."
This is the verdict of one seasoned military observer who has closely followed Nato's unfolding operations in Helmand province.
British and other Nato forces are often involved in sometimes grinding combat. They are suffering casualties.
But they say they are inflicting many more on their Taleban opponents.
"This war is winnable," says one source, "but both the British and Nato as a whole need more resources."
The debate in Britain is especially lively. The loss of a Royal Air Force Nimrod reconnaissance aircraft with its 14-strong crew on Saturday has been followed by further losses for the Nato-led force in Afghanistan.
Too few men
The casualties come at a time when British troops in particular have been engaged in some serious fighting.
But this is not exclusively a British problem - the Canadians too have had combat casualties.
And, to an extent, the losses serve to underline weaknesses in the Afghanistan operation as a whole.
There have been shortages of equipment from the outset.
But it is troops on the ground who are in the shortest supply.
And some insiders fear that these shortcomings could leave large areas beyond effective government control.
The essence of the problem is the essential contradiction of counter-insurgency operations.
Military success is essential to shape the conditions for a more stable society.
But military operations in themselves cannot deliver better governance and development projects.
All the military can do is to create an environment in which the Afghan government and other agencies can expand the rule of law, healthcare, better water supplies and so on.
This really is a battle for the hearts and minds of ordinary people.
And success here requires not just the defeat of Taleban units in individual engagements, but a continuing presence from Nato troops to ensure that the Taleban fighters don't simply return once the foreign troops are gone.
Sources contacted by the BBC say that the British simply do not have sufficient men both to hold areas cleared of Taleban fighters and to mount mobile offensive operations.
The nature of the terrain, the altitude and the complexity of communications impose punishing strains upon both men and equipment. More troops may well be needed. But the question is, from where will they come?
Britain - with ongoing operations in Iraq and elsewhere, is clearly hard pressed to come up with additional soldiers, at least for any sustained period.
The new head of the British Army, General Sir Richard Dannatt, has told the Guardian newspaper that his forces are only just coping with their multiple commitments.
If there are to be reinforcements then they will have to come from other Nato countries.
British Foreign Office Minister Kim Howells, speaking during a visit to Afghanistan, said that he would like to see many more troops and resources deployed. He said he hoped Nato would see the urgency of the situation.
Both government ministers and senior military commanders are walking a tightrope in terms of what they can say in public.
Nonetheless the signals are clear. The military element of the international campaign in Afghanistan is at risk of stalling for want of sufficient resources.
Winning engagements and inflicting serious casualties on the Taleban are essential but not sufficient conditions for victory.
Up to now, Nato countries have only grudgingly released troops for high-intensity operations.
And with several key alliance-members already heavily involved in the UN's Lebanon operation, reinforcements for Afghanistan may be hard to come by.