"A military operation has begun in the western areas of Anbar to liberate them from Daesh," said Lieutenant General Qassem Mohammedi, commander of the Jazeera Operations Command, using an Arabic acronym for IS.
He said the operation was led by the army's 7th division, police, and fighters from local tribes that have opposed the jihadists, with aerial backing from the US-led coalition.
The main targets of the operation are Aanah, Rawa and Al-Qaim, the westernmost Iraqi towns along the Euphrates Valley.
"Our forces started advancing from Haditha towards Aanah from several directions," Mohammedi told AFP.
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Haditha was never seized by IS when the group swept across much of Iraq's Sunni Arab heartland in 2014 and is home to a tribe that has led the fight against the jihadists in the area.
"Zero hour has come to liberate the western areas," Nadhom al-Jughaifi, a commander with the Haditha tribal fighters, said.
Anbar is a desert area traversed by the Euphrates that borders Saudi Arabia, Jordan and Syria. Security in reconquered areas remains precarious and jihadists continue to move across the province.
Tens of thousands of Iraqi forces are currently involved in an offensive to retake Mosul, the main northern city which is also IS's last major stronghold in the country.
IS has lost more than half of the territory it once controlled in Iraq and the loss of Mosul would deal a major blow to the "caliphate" it proclaimed there in June 2014.