Even as its civilian leaders publicly decried US drone attacks as breaches of sovereignty and international law, Pakistan's top intelligence agency secretly worked for years with the CIA on strikes that killed Pakistani insurgent leaders and scores of suspected lower-level fighters, according to classified US intelligence reports.

Dozens of civilians also reportedly died in the strikes in the semi-autonomous tribal region of Pakistan bordering Afghanistan that is a stronghold of al-Qaeda, Afghan militants, other foreign jihadists and a tangle of violent Pakistani Islamist groups.

On the home front: Pakistani demonstrators shout anti-US slogans during a protest against drone strikes earlier this year. Credit:AFP

Copies of top-secret US intelligence reports reviewed by McClatchy Newspapers provide the first official confirmation of joint operations involving drones between the US spy agency and Pakistan's powerful army-run Inter-Services Intelligence Directorate, or ISI, as well as previously unknown details of that co-operation. The review takes on important significance as the administration reportedly is preparing to expand the use of drones in Afghanistan and North Africa amid a widespread debate over the legality of the strikes in Pakistan.

The documents show that while the ISI helped the CIA target al-Qaeda, the US used drone strikes to aid the Pakistani military in its battle against the Taliban Movement of Pakistan, or TTP, assistance the Obama and Bush administrations never explicitly acknowledged or legally justified.