BAGHDAD (Reuters) - Iraq's army said on Sunday it was preparing to retake the Islamic State (ISIS) stronghold of Falluja and asked residents to get ready to leave, state TV reported.

Families who could not leave should raise white flags to mark their location in the city just went of Baghdad, the army's media unit added, according to the TV channel.

Falluja was the first Iraqi city to fall to ISIS in January 2014, six months before the group that emerged from Al-Qaeda swept through large parts of Iraq and neighbouring Syria.

The army "is asking the citizens that are still in Falluja to be prepared to leave the city through secured routes that will be announced later," the channel said.

The city on the Euphrates river 50 km west of the capital, had a pre-war population of around 300,000.

It is encircled by Iraqi forces and a coalition of Shi'ite militias known as Hashid Shaabi.

Known as the "City of Minarets and Mother of Mosques", Falluja is a focus for Sunni Muslim faith and identity in Iraq. It was badly damaged in two offensives by US forces against Al-Qaeda insurgents in 2004.