The administration of President Barack Obama is completing a counterterrorism manual that will establish clear rules for targeted-killing operations, The Washington Post reported.
But citing unnamed US officials, the newspaper said the guidebook would contain a major exemption for the CIA's campaign of drone strikes in Pakistan.
This exemption will allow the Central Intelligence Agency to continue striking Al-Qaeda and Taliban targets in Pakistan for a year or more before the agency is forced to comply with more stringent rules spelled out in the document, the report said.
According to the London-based Bureau of Investigative Journalism, between 2,627 and 3,457 people have been reportedly killed by US drones in Pakistan since 2004, including between 475 and nearly 900 civilians.
The covert strikes are publicly criticized by the Pakistani government as a violation of sovereignty but American officials believe they are a vital weapon in the war against Islamist militants.
Few of the victims are publicly identified.
The manual is expected to be submitted to Obama for final approval within weeks, the paper said.
The Post said the adoption of a formal guide to targeted killing marks a significant milestone: the institutionalization of a practice that would have seemed anathema to many before the September 11, 2001 attacks.
The subjects covered in the playbook include the process for adding names to kill lists, the legal principles that govern when US citizens can be targeted overseas and the sequence of approvals required when the CIA or US military conduct drone strikes outside war zones, the paper said.
According to The Post, the effort to draft the playbook was nearly derailed late last year by disagreements among the State Department, the CIA and the Pentagon on the criteria for lethal strikes.
They led to granting the CIA a temporary exemption for its Pakistan operations as a compromise that allowed officials to move forward with other parts of the playbook.