Iraqi state TV declared the start of the operation, in which troops will be backed by Shiite and Sunni paramilitary forces, but did not provide further details.
The Islamic State group seized large parts of Anbar starting in early 2014 and captured Ramadi earlier this month. The fall of the city marked a major defeat for Iraqi forces, which had been making steady progress against the extremists over the past year with the help of US-led airstrikes.
Security forces and Sunni militiamen who had been battling the extremists in Ramadi for months collapsed as ISIS fighters overran the city. The militants gained not only new territory 115km west of Baghdad, but also large stocks of weapons abandoned by the government forces as they fled.
The capture of Ramadi was a major blow to the US-backed strategy against the Islamic State group. Defense Secretary Ash Carter said Sunday that Iraqi forces had "vastly outnumbered" the ISIS militants in Ramadi but "showed no will to fight."
Saad al-Hadithi, a spokesman for Iraq's Prime Minister Haider al-Abadi, said the government was surprised by Carter's remarks, and that the defense secretary "was likely given incorrect information."
Al-Abadi has called on Shiite militias to help Iraqi troops retake the Sunni province of Anbar. The militiamen have played a key role in clawing back territory from the ISIS group elsewhere in Iraq but rights groups accuse them of looting, destroying property and carrying out revenge attacks. Militia leaders deny the allegations.
