A long term Western presence in Afghanistan may provoke "a local backlash against foreign meddling", a former foreign secretary has warned

Lord Hurd, who was foreign secretary to John Major during the height of the Yugoslavia crisis, said it was difficult to pass judgement on a peacekeeping operation set up both to counter terror and reconstruct Afghan society.

Reflecting broader concerns about the scope of the West's commitment in Afghanistan, Lord Hurd expressed concern that a lack of clarity could lead to an Afghan backlash against foreign troops.

"If for example, we are to stay in Afghanistan, we need to be clear of the purpose," he said.

"Is it to deny al Qaeda the use of those caves and mountains to prepare and commit acts of terrorism? Is it to help the present Afghan government cope with warlords and traffickers in heroin? Is it more widely to help Afghans build a democratic civil society?

"Are American and European answers to these questions the same?

"The wider our objective the longer it will take to achieve, and the greater meanwhile the risks of a local backlash against foreign meddling."

Widely criticised for his "hands off" approach in the Bosnia civil war, the peer's note of caution mirrors wider disquiet at the increasing number of Western military commitments abroad.

"The change in international attitudes is illustrated by the remark which the prime minister often makes about Afghanistan, when he says that this time we will not walk away," Hurd told the John Smith Memorial Trust Lecture at the Royal Museum of Scotland.

Hurd noted that the history of Afghanistan is a history of struggle against colonial occupiers, from the British Empire to the Soviet Union.

"Walking away is precisely what, for most of the last two centuries, the Afghans have dearly wanted the outside powers to do," he said.

Hurd warned that the longer the presence, the greater the commitment will be.

"As we have discovered in Cyprus, the longer an international force remains, the more difficult it becomes to withdraw it," he said.

"The act of intervention requires a moment of courage. Defining and sustaining that intervention, which can so easily be resented as occupation, requires patience and cool thought a different sort of courage."