Iraqi forces have launched an offensive to retake the Islamic State stronghold of Fallujah, after warning residents to leave before the fighting started.
"Zero hour for the liberation of Fallujah has arrived. The moment of great victory has drawn near and Daesh has no choice but to flee," Iraqi Prime Minister Haider al-Abadi said on his official Twitter feed, using an Arabic acronym for the jihadist group.
He said the offensive would be conducted by the army, police, counterterrorism forces, local tribal fighters, and a coalition of mostly Shiite Muslim militias.
The US-led coalition that has bombed Islamic State in Iraq and neighbouring Syria for nearly two years was expected to provide air support.
Fallujah, a longtime bastion of Sunni Muslim jihadists 50 kilometres west of Baghdad, was the first city to fall to the jihadists.
Islamic State took control of the city in January 2014, six months before the group declared a caliphate spanning large parts of Iraq and Syria.
Iraqi officials said Shiite militias, including ones backed by neighbouring Iran, may be restricted to operating outside the city proper, as they were largely in the battle for Ramadi, to avoid aggravating sectarian tensions with Sunni residents.
The Iraqi army, police and the militias, backed by coalition air strikes, have surrounded Fallujah since late last year, while the jihadists have been preventing residents from leaving for months.
Families who cannot flee should raise white flags to mark their location in the city, the military's media unit said in a statement on state television, a tactic employed with some success in other recent offensives.
Deputy District Council chairman Falih al-Essawi said three corridors would be opened for civilians to camps west, southwest and southeast of the city, and a subsequent military statement said some residents had begun to flee.
"Our goal is to liberate civilians from Daesh's repression and terrorism," Mr Abadi said in a televised speech.