Kabul: The US military said in a secret report the Taliban, backed by Pakistan, are set to retake control of Afghanistan after Nato-led forces withdraw from the country, raising the prospect of a major failure of western policy after a costly war.

Lieutenant Colonel Jimmie Cummings, a spokesman for the Nato-led International Security Assistance Force, confirmed the existence of the document, reported by Britain's Times newspaper and the BBC. But he said it was not a strategic study.

"The classified document in question is a compilation of Taliban detainee opinions," he said. "It's not an analysis, nor is it meant to be considered an analysis."

Nevertheless, it could be interpreted as a damning assessment of the war, now dragging into its eleventh year and aimed at blocking a Taliban return to power.

It could also be seen as an admission of defeat and could reinforce the view of Taliban hardliners that they should not negotiate with the US and President Hamid Karzai's unpopular government while in a position of strength.

The US military said in the document Pakistan's powerful Inter-Services Intelligence (ISI) security agency was assisting the Taliban in directing attacks against foreign forces.

The allegation drew a strong response from Pakistani Foreign Ministry spokesman Abdul Basit. "This is frivolous, to put it mildly," he told Reuters. "We are committed to non-interference in Afghanistan."