The Pakistani security services are directly assisting the Taliban in Afghanistan and have direct influence over its leadership, according to a leaked report.
The claim is made in a secret Nato report seen by the BBC and derived from thousands of interrogations of "insurgents" captured by Nato forces.
It alleges the Taliban still has wide support among the Afghan people, and the Pakistan intelligence service (ISI) knows the whereabouts of the group's leaders. "Pakistan's manipulation of the Taliban senior leadership continues unabatedly," it notes.
Pakistan is a major recipient of US military aid and has always denied aiding the Taliban. The report states: "Afghan civilians frequently prefer Taliban governance over the Afghan government, usually as a result of government corruption."
A Nato spokesman told the BBC that the report was "a classified internal document that is not meant to be released to the public".
It is likely to harm an already tense relationship between Pakistan and the West. It comes as President Barack Obama has reignited the controversy over the CIA's deployment of drones in Pakistan, admitting their use for the first time.
"A lot of these strikes have been in [Pakistan's tribal areas]," Mr Obama said in an interview streamed live on YouTube. "For the most part, they've been very precise precision strikes against al-Qa'ida and their affiliates, and we're very careful in terms of how it's been applied."
Washington's use of drones in Pakistan has long been a source of anger for many Pakistanis. But Mr Obama said the leadership in Islamabad lacked the political will and capacity to take on extremists.