Daesh militants killed 21 civilians in Mosul in the last three days, most of them accused of collaborating with the Iraqi forces who are attacking the city, a medical source in Mosul said.
The city's forensic medical department was notified of the killings, the source said. No bodies have emerged, unlike last week when 20 corpses were strung up across Mosul in a public warning against cooperating with the army.
Human Rights Watch meanwhile said that Iraqi soldiers, militiamen and civilians had mutilated the bodies of Daesh militants south of Mosul.
A 100,000-strong alliance of troops, security forces, Kurdish Peshmerga and Shia militias, backed by US-led coalition airstrikes, has almost surrounded Mosul, Daesh's last major stronghold in Iraq.
Residents say most of Daesh's victims are dumped in mass graves outside Mosul because the militants deem their opponents apostates unworthy of religious funeral. Families only learn the fate of relatives from lists delivered to medics at the morgue.
The medical source said a new list of 21 names was handed over in recent days.
"As usual there were no bodies, just names of people executed by the organisation for a variety of reasons," the source said. "Now most of the killings are on charges of collaboration with the Iraqi security services."
Before the military campaign started on 17 October, people were detained and investigated for months. Now they were held for as little as two weeks before being released or killed – either shot, their throats slit or other methods, the source said.
The accelerated killings took place as Iraqi counter terrorism forces battle to expand their foothold in the city's eastern neighbourhoods.
Officers say their progress has been slowed by the presence of more than a million civilians still living in Mosul. But they say some of their operations have been assisted by information provided by residents about Islamic State military positions.