Iraq's army has told residents of Fallujah to get ready to leave before what may be an attempt to take the city back from the Islamic State of Iraq and the Levant group, state TV said.

Families who cannot leave should raise white flags to mark their locations, the army's media unit said, according to a broadcast on Sunday.

Fallujah was the first Iraqi city to fall to ISIL (also known as ISIS) in January 2014, six months before the group swept through large parts of Iraq and neighbouring Syria.

Iraqi army tells Fallujah residents to flee city

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

The city on the Euphrates River, 50km west of the capital, had a prewar population of about 300,000.

It is encircled by Iraqi forces and a coalition of Shia Muslim armed groups known as Hashid Shaabi.

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