NATO insisted Wednesday that the Taliban have been weakened as the alliance downplayed the impact of a leaked report showing the insurgents confident of victory once Western combat troops leave in 2014.

"The Taliban have suffered tremendous setbacks on the battlefield in the last year, and we know that they've lost a lot of ground and they've lost a lot of leaders," NATO spokeswoman Oana Lungescu told reporters.

Support for the Taliban is also "at an all-time low," she said, adding that Afghan security forces, which are meant to take over from NATO troops by the end of 2014, are "getting stronger and more capable every day."

The spokeswoman said she would not comment on a classified document but she added that it was "basically a summary" of statements made by Taliban detainees during interrogations.

"So it's what they think or what they would like us to believe they think," she said on the eve of a two-day meeting of NATO defence ministers in Brussels.

The NATO report, leaked to British media and based on interrogations of thousands of detainees, is quoted as saying the Taliban's "strength, motivation, funding and tactical proficiency remains intact," despite setbacks in 2011.

"Many Afghans are already bracing themselves for an eventual return of the Taliban," the report says, according to the The Times of London.

"Once ISAF is no longer a factor, Taliban consider their victory inevitable," it says, referring to NATO's International Security Assistance Force in Afghanistan.

The document also charges that the Pakistani intelligence service was secretly supporting the Taliban.

"This sort of allegations in general terms we've heard before, there's nothing new in them," Lungescu said.

She repeated NATO concerns about safe havens along the Afghan-Pakistani border.

"The security of Afghanistan and Pakistan is closely linked together, which is why Pakistan has an important role to play," Lungescu said.

"But this is a problem that we must all tackle together because it affects our security, the security of our forces in Afghanistan, the security of the Afghan population and the security of Pakistan."