Mosul Video Killing - Iraq Begins Investigation
The footage shows some men wearing military apparels throwing an unarmed man over a cliff.
They alleged soldiers also take aim at his lifeless body.
An interior ministry spokesman said that if the video was authentic those responsible must be brought to justice.
Human rights groups say they have received numerous witness reports of torture and executions in Mosul.
Iraq's prime minister declared victory over IS in the city on Monday, after a nine-month battle that left large areas in ruins, killed thousands of civilians and displaced more than 920,000 others.