The Iraqi air force on Friday dropped leaflets calling on the population in the Daesh-held Old City centre of Mosul to flee, raising fears among humanitarian organisations for the safety of civilians.
The leaflet drop, announced in an Iraqi military statement, is an indication that the offensive to dislodge the militants from their remaining enclave in the northern Iraqi city was imminent.
The US-backed offensive on Mosul, now in its eighth month, has taken longer than planned as the militants are dug in among civilians.
Civilians trapped behind Daesh lines face a harrowing situation with little food and water, no electricity and limited access to hospitals.
"Iraqi air force planes dropped hundreds of thousands of leaflets a short while ago on the non-liberated areas ... urging citizens to exit through safe corridors," an Iraqi military statement said.
Concerns over safety of civilians
Prime Minister Haider al Abadi had initially hoped Mosul would be "liberated" by the end of 2016.
The fall of Mosul would mark the end of Iraqi half of the "caliphate" declared nearly three years ago by Daesh leader Abu Bakr al Baghdadi, which also covers parts of Syria.
Expecting an assault, about 700,000, nearly a third of the pre-war city's population, have already fled since October 2016, seeking refuge either with friends and relatives or in camps.
The United Nations last week said up to 200,000 more people could flee Mosul as fighting now moves to the Old City.
UN aid chief Stephen O'Brien on Friday said he was "deeply concerned" for the safety of civilians living under Daesh control, citing reports of families being shut inside booby-trapped homes and snipers targeting children.
"As many as 200,000 additional people may try to leave in the coming days," said O'Brien in a statement.
"Those who choose to flee their homes to access assistance must be free to do so without hindrance," he said.
UN agencies have set up camps near Mosul to house those displaced by the fighting and last summer estimated that up to one million people could be forced from their homes.