A secret U.S. military report says the Taliban, heavily backed by Pakistan, are confident they can win the Afghanistan conflict, and that they are gaining popular support at the expense of the Kabul government.

The report, The State of the Taliban 2012, is the latest of a series drawn up by a U.S. special operations task force on the basis of interrogations with 4,000 suspected Taliban and al-Qaeda detainees.

Its conclusions, that the Taliban's strength and morale are largely intact despite the NATO military surge, and that significant numbers of Afghan government soldiers are defecting to them, are in stark contrast to NATO's far more bullish official line, that the insurgent movement has been severely damaged and demoralized.

The report, leaked to the BBC and The (London) Times, also portrays the Taliban as being under the thumb of Pakistan's powerful security agency, the Inter-Services Intelligence (ISI), but resenting that control.

According to published excerpts, the report finds that "Taliban commanders, along with rank and file members, increasingly believe their control of Afghanistan is inevitable. Though the Taliban suffered severely in 2011, its strength, motivation, funding and tactical proficiency remains intact."