Air Force Brigadier General Richard Coe, who headed U.S. Central Command's investigation of the incident, called it "an unintentional, regrettable error, primarily based on human factors in several areas in the targeting process."
In a conference call with reporters, Coe said the mistaken identification of the forces as ISIS fighters "was made in good faith, based on information reasonably available at the time to all coalition decision makers" and carried out within the parameters of the law of armed conflict.
"I further found there was no intent to target Syrian forces and that the targets underwent an appropriate assessment, review and validation process," said Coe.
On September 17, American, British, Danish and Australian aircraft carried out a large strike on what was believed to be an ISIS camp south of the eastern Syrian city of Dayr az Zawr.
To the intelligence analysts reviewing video surveillance, the personnel at the camp "looked and acted like the forces the coalition has been targeting for the past two years" said Coe.
They were not wearing military uniforms and no unit flags or other military insignia were visible.
After the initial decision that the individuals at the camp were ISIS fighters, planning for the attack was completed in a matter of days.
Coe said investigators have been unable to determine precisely who was targeted in the attack other than labeling them as "forces aligned with the Syrian government."
The airstrike was called off after the Russian military alerted the Combined Air Operations Center in Qatar through a phone line established to coordinate air safety in Syrian airspace.
But there was a 27-minute delay in communicating the mistaken targeting, as the Russian officer who initiated the contact with the operations center did not disclose why he was calling until he spoke with his designated American counterpart.
Recommendations from Coe's report to reduce the risk of human error in future airstrikes, he said, are already being implemented.