The operation has been in the works for days with Iraqi aircraft carrying out strikes and forces massing for the drive toward Amerli.
The town has been besieged since militants from the so-called Islamic State of Iraq and the Levant (ISIL) terrorist group launched a major offensive in June.
Residents face major shortages of food and water, and are in danger both because of their Shiite faith, which ISIL terrorist consider heresy, and their resistance to the militants.
Army Staff Lieutenant General Abdulamir al-Zaidi said the operation to free Amerli from the ISIL terrorists has been launched with support from Iraqi aircraft, vowing that "we will be victorious over them".
And Karim Mulla Shakur, a Kurdish political party official, said that Kurdish fighters were also involved.
UN Iraq envoy Nickolay Mladenov has called for an urgent effort to help Amerli, saying residents face a "possible massacre" if the town is overrun.
RA/SHI