Defense chiefs revealed in a media briefing on Wednesday, that the Super Hornet pilots and their commanders stopped pursuing their IS target when it moved into a populated urban area.
Vice Admiral David Johnston, Chief of Joint Operations, said the jet fighters, which were providing air cover to Iraqi forces on the ground on Sunday night, put the safety of civilians first.
"One of our [Super Hornet] packages on the first night ... had an identified target which it was tracking and that particular target moved into an urban area where the risks of conducting a strike on that target increased to a point where it exceeded our expectations of collateral damage, so they discontinued the attack at that point," he told reporters.
He said IS militants were "not moving as freely as they were" since the air strikes began.