Nato forces engaged in a bloody battle against the Taleban are not just fighting for control of southern Afghanistan, but for the future existence of the alliance itself.

What began as a bold mission to confront Islamic militants half way around the world, has now turned into a fierce struggle that is straining the bonds that have tied the 26 members states together for the past half century.

Nato members often boast that the organisation is the most successful and most powerful defensive alliance ever assembled in military history.

Yet a week after General James Jones, the US Supreme Allied Commander Europe, requested 2,500 additional combat troops to serve in Afghanistan none of the member states has produced a single soldier.

The seriousness of the crisis was highlighted on Tuesday by Jaap de Hoop Scheffer, the Nato secretary-general, who made an embarrassing public appeal for member states to fulfil their obligations.

"The question here is...that nations should live up to what they promised," he told the BBC Radio 4 Today programme. "I have called, and I am calling in front of your microphones, for alliance solidarity because some nations are carrying more of the burden than others."

The plea has gone unanswered. Instead it has touched off an angry debate about who is sacrificing the most.

Many Nato countries have been directly involved in the US-led war on terror for the past five years. Fatigue is setting in. Forces are overstretched. The conflict shows no signs of ending any time soon.

There is a growing perception among the public in Europe that the Bush Administration has mishandled the conduct of the conflict and that Iraq, and now possibly Afghanistan, may defeat the cream of the Western military.

Those fears are reflected in the conduct of the war in southern Afghanistan, which was meant to be a Nato peacekeeping mission but instead has turned into a deadly counter-insurgency war.

American, British, Canadian and Dutch troops are taking the brunt of the fighting, and the casualties, in southern Afghanistan.

Britain, which has already had to reinforce its contingent, which now stands at 5,400 is particularly, feels particularly let down.

Tony Blair said yesterday: "We have made our contribution... if you talk to Nato they recognise that."

But other major contributing states insist they are contributing just as much to the fight.

Italy has forces deployed in Afghanistan, Iraq, the Balkans and is making the biggest contribution to the United Nations peacekeeping effort in southern Lebanon. France and Spain are in similar positions.

Germany has 2,700 troops in Afghanistan, albeit in the quieter northern region, but officials bristle at the suggestion that they are not pulling their weight.

"This is not a situation where we can simply withdraw some forces," said a German military source. "The north is not some kind of safe billet."

The issue may be resolved next week at the United Nations General Assembly when Nato foreign ministers meet to discuss the crisis.

The Americans and British are hoping that Poland, which was one of the main contributors to the military mission in Iraq, will come up with the necessary reinforcements. They have pledged an extra 900 troops for the mission today.

If Nato can cobble together the necessary troops, then the divisions in the alliance can be papered over. But the crisis does not bode well for future operations. By most accounts the war in Afghanistan is likely to continue for years to come.

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