The operation, which Iraqi state TV said was backed by Shiite militias and Sunni pro-government fighters, is deemed critical in regaining momentum in the fight.
But as a sandstorm descended across the region, there was no sign of any major engagement against the extremists, who have been gaining ground in the province west of Baghdad despite US-led airstrikes.
A Pentagon spokesman, Col. Steve Warren, said Iraqi forces have begun "shaping operations" and "security zone interactions," which he described as probing and reconnaissance actions that would precede any major combat in or around Ramadi.
The Islamic State also known by the acronyms ISIS and ISIL, and Daesh in Arabic seized large parts of Anbar in early 2014 and captured Ramadi earlier in May. Iraqi forces, which had been making steady progress against the extremists in recent months with the help of the air campaign, scored a major victory in recapturing Saddam Hussein's hometown of Tikrit last month.
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The launch of the operation in Anbar came only days after US officials, including Defense Secretary Ash Carter, criticized Iraq's forces, saying its troops fled the IS advance on Ramadi without fighting back, leaving behind weapons and vehicles for the extremists.
Baghdad defended its troops and said preparations were underway for the large-scale counteroffensive in Anbar, involving Iranian-backed Shiite militias known as Popular Mobilization Units. That possibility sparked fears of potential sectarian violence in the Sunni-dominated province, long the site of protests and criticism of the Shiite-led government in Baghdad.