As it continues to lose ground to Iraqi-led coalition forces, the Islamic State (ISIS) is lashing back at the remaining civilians in the areas it still controls, using even more brutal measures to intimidate and coerce them.

In the latest report of ISIS atrocities, three women who refused an order by the militants to "slaughter" fellow civilians were burned alive in Mosul, Iraqi News reported, citing eyewitness accounts.

The civilians had been caught trying to flee from the Wadi Akab area west of Mosul.

In previous similar incidents, the ISIS punished the escapees by ordering its own militants to execute them. This time though, the witnesses said, the ISIS asked the three civilian women to execute the escapees themselves.

When they refused the direct command, the ISIS militants ordered them executed instead by burning them alive. The sources did not say what happened to the escapees who were supposed to be executed.

In January this year, the ISIS reportedly burned alive a mother and her four children who were caught fleeing the caliphate.

The four children comprised of three girls and a nine-month-old boy. They were caught by ISIS militants in Hawija on their way to Kirkuk, a source told Iraqi News.

Upon capture, the mother and her children were bound, doused with petrol, and set ablaze, the source said, adding that this was done in front of a group of civilians.

News of the latest ISIS atrocity came as Iraqi-led coalition forces continue to gain more ground in their assault on the ISIS stronghold of Mosul.

The United Nations High Commissioner for Refugees has warned that "the worst is yet to come" as the coalition prepares for its final push to completely liberate the city, the second biggest in Iraq after Baghdad, from the jihadists.

The U.N. refugee agency estimates that about 400,000 residents remain trapped in Mosul's Old City, while as many as 600,000 remain trapped in Western Mosul, Reuters reported.

Bruno Geddo, a UNHCR representative in Iraq, told a news briefing that the people of Mosul are panicking and "desperate for food."

"The more you go without food, the more you become panicked and the more you want to run away," he said.

He said the trapped residents are resorting to various ways to escape Mosul without being spotted by ISIS fighters.

"We also heard stories of people running away under the cover of early morning fog, running away at night, of trying to run away at prayer time when the vigilance at ISIS checkpoints is lower," Geddo said.