Abu Bakr al-Baghdadi may be "losing command and control" of ISIL militants in Mosul, a US spokesperson has said.

Colonel John Dorrian’s comments follow the release of an audio message, purportedly made by the leader, in which he calls on his fighters in the Iraqi city to "wreak havoc."

"It is quite clearly an effort on the part of Daesh (ISIL) to communicate to their fighters. And this is probably excellent evidence that their command and control and ability to communicate directly with their fighters and control them has been severely reduced," said the colonel.

He re-confirmed that only Iraqi troops would enter the ISIL stronghold for now, leaving coalition forces, including Kurdish Peshmerga fighters, Sunni Arabs and Shia Muslim militiamen on the outskirts of the city.

Amnesty International reports men and boys suspected of having links to the jihadists have been tortured in revenge attacks carried out by militia fighters from the Sab’awi tribe.

While forces are press forward on the eastern and southern outskirts of Mosul, more and more people are fleeing.

However, aid agencies say that more than one million civilians are still inside the city. As Iraqi special forces claim ISIL is using so-called flying bombs, the Norwegian Refugee Council has warned those remaining in Mosul are in "grave danger."