WASHINGTON -- Even as its civilian leaders publicly decried U.S. drone attacks as breaches of sovereignty and international law, Pakistan’s premier 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 U.S. 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 Qaida, Afghan militants, other foreign jihadists and a tangle of violent Pakistani Islamist groups.

Copies of top-secret U.S. intelligence reports reviewed by McClatchy provide the first official confirmation of joint operations involving drones between the U.S. spy agency and Pakistan’s powerful army-run Inter-Services Intelligence Directorate, or ISI, as well as previously unknown details of that cooperation. 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 Qaida, the United States used drone strikes to aid the Pakistani military in its battle against the Taliban Movement of Pakistan, or TTP – assistance that the Obama and Bush administrations never explicitly acknowledged or legally justified.

The White House did not respond immediately to a request for a comment on McClatchy’s findings. The Pakistani government denied there was ever any cooperation on drone strikes.

The partnership was so extensive during the Bush administration that the Pakistani intelligence agency selected its own targets for drone strikes. Until mid-2008, the CIA had to obtain advanced approval before each attack, and under both administrations, the Pakistanis received briefings and videos of the strikes.

The U.S. intelligence reports illustrate how the Pakistani army retained its grip on national security policy after 2008 elections ended the nation’s fourth bout of military rule and brought to power a civilian government, which condemned drone strikes as violations of Pakistan’s sovereignty and international law. The strikes killed hundreds of civilians and produced new recruits for Islamist extremist groups, charged the government, which resigned last month in advance of May 11 parliamentary voting.

What remains unclear is the degree to which the government under President Asif Ali Zardari, which tried unsuccessfully to wrest control of the ISI from the military, acquiesced in the CIA-ISI collaboration.

The ISI is a domestic and international spy and paramilitary service that officially reports to Pakistan’s prime minister. In reality, however, the agency answers to the chief of staff of the army, which has ruled Pakistan for most of its 66 years. Former Prime Minister Yousuf Raza Gilani in 2011 called the army a “state within a state.”

Traditionally commanded by an army general and mostly staffed by military officers, the ISI has an ominous reputation as the Pakistani army’s instrument for rigging elections and crushing internal dissent. It has been accused of directing proxy wars and terrorist attacks by Islamist extremists in India and on civilians and U.S.-led troops in Afghanistan.