The revised Law of War Manual gives examples of precautions the US military should take to avoid civilian deaths, such as providing warnings and conducting detailed assessments of potential casualties.
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"Protecting civilians in armed conflict is critical, and it's important that our legal guidance is clear and practical," Pentagon General Counsel Jennifer O'Connor said in a statement.
"This version of the manual provides greater clarity and also reflects important developments such as the president's recent executive order on civilian casualties."
President Barack Obama in July released an executive order that provides additional information on "best practices and procedures" that can be applied to air strikes.
During his campaign, President-elect Donald Trump, who takes office on January 20, suggested he would loosen rules of engagement in the ongoing war against Islamic State militants.
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The manual also includes new discussion of the principle of "proportionality" -- aimed at avoiding "unreasonable" use of force.
Tuesday's changes are the latest in a series of updates to the Law of War Manual.
Media organisations blasted the Pentagon in 2015 when the document said reporters could be treated as "unprivileged belligerents."
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The Pentagon has since altered the language to emphasize the protection of journalists as civilians, and "to clarify that a journalist can only be considered a combatant on an exceptional basis when that person had acquired such status."
For instance, journalist protections do not extend to members of non-state armed groups being used for propaganda purposes, the manual states.
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