Iraqi forces pressed forward on Monday with a broad offensive targeting Islamic State group-held areas in west Mosul and called for civilians to leave areas where fighting is taking place.

More than seven months into the massive operation to recapture Mosul from IS, Iraqi forces have retaken the city's east and large parts of its western side, but the jihadists are still putting up tough resistance.

"Our units are continuing to advance… and entered Al- Saha al-Oula and Al-Zinjili and Al-Shifaa neighbourhoods and the Republican Hospital," said Joint Operations Command spokesman Yahya Rasool.

IS was using "explosives-rigged vehicles and snipers and suicide bombers" to target Iraqi forces, he told AFP.

The areas mentioned by Rasool — which are located north of Mosul's Old City, where IS also still holds significant territory — are the main targets of the offensive, which was announced on Saturday.

The Joint Operations Command also said today that Iraqi aircraft had dropped leaflets over Mosul urging residents to leave IS-held areas — the second time this was done within the past week.

Overnight, planes dropped "thousands of leaflets on the Old Mosul, Al-Zinjili, Al-Shifaa and Al-Saha areas urging citizens to leave toward our security forces," it said.

This is the opposite of the strategy Iraqi forces employed in east Mosul, where they urged civilians to stay in their homes.

International aid organisation Save the Children has said it is "deeply concerned that any calls to leave west Mosul will mean that civilians, particularly children, are in significant danger of being caught in the crossfire." 

Asked about the change in tack, Rasool noted that the western side of the city has a greater population density as well as "old areas," an apparent reference to the Old City.

The area — a warren of closely spaced buildings and narrow streets — has posed a significant challenge to Iraqi forces, which have surrounded it with a large number of civilians trapped inside.

"The Old City has been blockaded for a while, completely from the south and now our units are present on the north and west," he said, while the area's eastern side is bordered by the Tigris River.

The battle for Mosul has taken a heavy toll on civilians, pushing hundreds of thousands to flee, while hundreds more have been killed or wounded.

On Thursday, the United States announced the results of an investigation into a deadly coalition air strike earlier this year.

The probe found that at least 105 civilians had been killed and 36 remained unaccounted for after the strike detonated IS-planted explosives.