British troops are a long way from winning the battle against a resilient Taliban in Afghanistan, and the conflict in the country could lead to "major shifts" in military spending, said British Defence Secretary Bob Ainsworth.
"We are facing a resilient enemy which we are far from succeeding against yet," he told an audience of defence experts at King's College, London.
"I reject the proposition we are not making progress. I also reject the proposition a reduced military presence will lead to less Taliban success," The Telegraph quoted Ainsworth, as saying.
A leading think-tank warned earlier that the presence of large numbers of foreign troops in Afghanistan made it harder to achieve a political settlement to the conflict. The International Institute for Strategic Studies said Western forces in Afghanistan needed a "more cunning" strategy if they were to achieve their aims.
Ainsworth said a military failure in Afghanistan would have "profound consequences for our national security" and "undermine the NATO alliance".
He also called for an open debate about future defence policy and how money for the military should be spent before the government publishes a defence review green paper in advance of next year's general election.