Nato has "lost in Afghanistan" and its failure to bring stability there could provoke a regional sectarian war "on a grand scale", according to Lord Ashdown.
The former United Nations High Representative for Bosnia and Herzegovina delivered his dire prediction after being proposed as a new "super envoy" role in Afghanistan.
Lord Ashdown said: "We have lost, I think, and success is now unlikely."
The assessment will be considered extreme by some diplomats but timely by those pressing for more resources for Nato operations.
Lord Ashdown added: "I believe losing in Afghanistan is worse than losing in Iraq. It will mean that Pakistan will fall and it will have serious implications internally for the security of our own countries and will instigate a wider Shiite [Shia], Sunni regional war on a grand scale.
"Some people refer to the First and Second World Wars as European civil wars and I think a similar regional civil war could be initiated by this [failure] to match this magnitude."
Lord Ashdown, 66, the former leader of the Liberal Democrats, was speaking in advance of a Nato summit in the Dutch town of Noordwijk yesterday…
Our Servicemen are done a great disservice by Lord Ashdown when he claims that we are losing the war in Afghanistan. In the year that British forces have been fully operational in southern Afghanistan, they have fought some of the fiercest engagements since Korea, and have comprehensively defeated their Taliban foes at virtually every turn.
They have also taken significant casualties, with 82 killed and scores more suffering severe injuries since British troops were first deployed to Afghanistan in 2001: 2nd Bn Mercian Regiment, which returned home yesterday, has itself lost nine men during its six-month tour of duty, which is now par for the course for British units serving on the front line in the war on terror.
But while, in strictly military terms, British forces and their allies are prevailing in their war to subjugate the Taliban, they are not enjoying the same degree of success in the other, and arguably more important, aspect of their mission assisting the Afghan people in the reconstruction of their country.
The main reason for this lack of progress is the continuing failure of many Nato states to provide sufficient numbers of combat troops….
The Government is considering sending more troops to Afghanistan to make up for the expected withdrawal of other Nato forces, a spokesman for the organisation has said.
Gordon Brown has repeatedly said that the reconstruction of Afghanistan is central to British foreign policy
Britain already has 7,700 soldiers fighting Taliban insurgents in Helmand province, at a time when senior Army officers complain that there is a serious overstretch in the armed forces.
There are fears that the Canadian and Dutch governments may withdraw their forces because of growing political pressure…