Thousands of people are fleeing the Iraqi city of Mosul, held by the so-called Islamic State (IS) group, in fear of US-led air strikes and fierce fighting by Iraqi ground troops.

Dozens of people were reported buried in wreckage after an air strike in western Mosul earlier in the week.

Other residents say IS is using civilians as human shields, hiding in houses and forcing young men to fight.

The offensive to recapture Mosul from IS began last October.

One resident who escaped Mosul, Muna, told our correspondent that hundreds of bodies remained under rubble. She lost nine members of her family.

The army is now closing in on the densely populated Old City of Mosul in the western half. A large plume of smoke could be seen hanging over the area.

Multiple air strikes were launched on Saturday morning.

The United Nations has already said that it is concerned about high numbers of civilian casualties.

Iraqi security forces, with the help of Kurdish Peshmerga fighters, Sunni Arab tribesmen and Shia militiamen, retook eastern Mosul in January.

Concern at the plight of civilians prompted a senior UN official on Friday to decry the “terrible loss of life” after claims that dozens of people had been killed in an air strike.

US media reports say an investigation is under way. It is not known exactly when the deaths are alleged to have occurred.

But reporters in western Mosul’s Jadideh neighbourhood said they saw 50 bodies being pulled out of rubble on Friday, after the buildings were razed in air attacks earlier in March.

• More than 180,000 flee west Mosul battle
• Battle for Mosul: The story so far
• ‘Prisoners’ remains’ in Mosul mass grave

The New York Times quoted US military officials saying the coalition was investigating reports of civilian deaths from a strike between 17-23 March.

The UN estimates that 400,000 Iraqi civilians are trapped in the Old City of Mosul. US officials believe there are about 2,000 IS fighters left in western Mosul.