The US government has released a once-secret policy document once dubbed "the playbook" that shows how officials select drone targets in areas outside war zones and the key role the president has in the process.

The 18-page Presidential Policy Guidance (PPG), published Saturday by the American Civil Liberties Union, provides more details than the government had previously revealed on how drone strikes are approved.

"Actions, including lethal action against designated terrorist targets, shall be as discriminating and precise as reasonably possible," the PPG states.

President Barack Obama typically must personally sign off on plans to strike terror suspects who are located outside war zones in which America is officially fighting. Such zones include Pakistan, Libya, Somalia and Yemen.

Strikes in combat theaters such as Iraq, Syria and Afghanistan are controlled by the military.

Each case for action is subjected to legal review before it goes to the National Security Council and then the president.

The policy document says that "absent extraordinary circumstances," a drone strike on a high-value target will only be taken if there is "near certainty" no civilians will be killed, and says the United States should respect another nation's sovereignty in weighing drone strikes.

The partially redacted document was released as a result of a lawsuit brought by the ACLU, which has long sparred with the government over America's secretive drone program.

"The PPG provides crucial information about policies that have resulted in the deaths of thousands of people, including hundreds of non-combatants, and about the bureaucracy that the Obama administration has constructed to oversee and implement those policies," ACLU Deputy Legal Director Jameel Jaffer said in a statement.

"The release of the PPG and related documents is also a timely reminder of the breadth of the powers that will soon be in the hands of another president," he added.

Justice Department lawyers turned the document over to the ACLU late Friday, and the rights group released it publicly on Saturday.

The Obama administration last month provided fatality estimates for 473 strikes between 2009 and 2015 that were conducted outside principal war zones.

Officials claimed anywhere from 64 to 116 civilians were killed in the strikes, and up to 2,581 combatants -- but critics have constantly said the government underestimates civilian deaths.

National Security Council spokesman Ned Price stressed that the PPG offers protections to civilians that "exceed the requirements of the law of armed conflict."

He added that "near certainty" that the target is present, and that non-combatants will not be killed, was the "highest standard we can set."

"The president has emphasized that the US government should be as transparent as possible with the American people about our counterterrorism operations, the manner in which they are conducted, and their results," Price said in a statement.

"Our counterterrorism actions are effective and legal, and their legitimacy is best demonstrated by making public more information about these actions as well as setting clear standards for other nations to follow."

The PPG also outlines what should be done in the event a suspect is captured, stressing that in "no event" will a detainee brought to Guantanamo Bay -- the US military prison Obama has so far failed to close.