Whistleblowers accused the US military of manipulating intelligence data on its operations against ISIL prompting an investigation regarding the assessments.
The US military may have manipulated intelligence reports to create a more positive picture of its campaigns in Afghanistan, as well as against ISIL, according to recent reports.
Many of the concerns appear to be coming from intelligence officials inside the Defense Department, including Gregory Hooker, who resigned after blowing the whistle on the reports.
"A lot of the analysts at Centcom feel the high command has been sugarcoating their assessments," former senior intelligence official Gregory Hooker told Foreign Policy.
Many of the documents investigated are classified and some are said to have been destroyed before being forwarded to investigators. According to Hooker, the manipulations may have been made to such an extent that they even crossed a customary boundary between the military and intelligence agencies.
The cited manipulations included labeling Iraqi army retreats as "redeployments," according to the New York Times. The Iraqi army suffered considerable blows in 2014, when it lost Mosul, the country's third-biggest city, in just six days.
Rebelling analysts said that the military assessments glossed over important factors in ISIL's rise, such as political and religious divisions in Iraqi society.
The investigation may also undermine statistics released by the US Defense Department on its campaign against ISIL. The US military began publishing infographics detailing its successes against ISIL after Russia began a major airstrike operation against the group in Syria after a request by the country' government.
The US military initially responded with warnings against the Russian operation against ISIL in Syria, although the two bodies now have a direct line to coordinate their operations.