The safety of hundreds of thousands of civilians trapped in Mosul is a key priority, the UN has warned, as Iraqi troops prepare to attack Islamic State (IS) militants in the west of the city.
The UN humanitarian co-ordinator for Iraq, Lise Grande, told the BBC Iraq had made this its priority when it won back the east of the city.
But the western side, with its narrow streets, may prove a bigger challenge.
Leaflets warning residents of an imminent offensive have been dropped.
Mosul is the last major base of IS in Iraq, and the operation to drive the militant group from the city started in October.
Battle for trust
Iraqi government soldiers, Ms Grande said, "need to ensure that that humanitarian concept of operations is adhered to, and that all of the parties to the conflict do absolutely everything they can to ensure that civilians survive the battle, and that they live".
"Absolutely nothing is more important going into the campaign to retake western Mosul," she said.
Iraqi forces recaptured the eastern part of the city earlier this year and have now all but surrounded the western part.
The US-led coalition has been carrying out air strikes on IS targets.
Winning the city back has never been just about the military objective of driving IS out of its stronghold, the BBC's Sebastian Usher says.
Minimising civilian casualties and avoiding reprisals will be key to regaining the trust of the city's population in the Iraqi state itself, he adds.