The Iraqi Prime Minister Haider al-Abadi on Sunday, (19 February) announced the launch of a ground offensive in western Mosul to drive the Islamic State (Isis) out of the area.

"We announce the start of a new phase in the operation, we are coming to Nineveh to liberate the western side of Mosul. Our forces are beginning the liberation of the citizens from the terror of Daesh [IS]," he added.

The Iraqi air force has reportedly dropped leaflets on western Mosul warning its residents of an impending ground offensive to oust the IS (Daesh) from the area, the Iraqi defence ministry said in a statement, Reuters reported.

The statement said the leaflets "contain instructions for the citizens to get ready to welcome the Iraqi forces that are coming to liberate their areas and to warn the Daesh (Islamic State) members to lay down their weapons and surrender".

At least 650,000 civilians in western Mosul are under siege along with the Isis militants. The US backed Iraqi forces were successful in ousting the terrorist group from the eastern part of Mosul in a battle that came to an end in January and now have all but surrounded the western side.

Meanwhile, the United Nations has warned that the safety of the thousands of civilians trapped in the area is a top priority.

Lise Grande, the UN humanitarian co-ordinator for Iraq told the BBC that it had made the safety of civilians its top priority when the Iraqi forces waged an offensive to take back eastern Mosul.

She added that the Iraqi forces "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," Grande said.

According to reports, retaking western Mosul could prove to be a bigger challenge due to its narrow streets.