Islamic State has seized and killed dozens of people in areas around Mosul that it still controls in an apparent bid to quell opposition and instil fear as opposition forces march on the group’s last Iraqi stronghold.

The United Nations, Kurdish forces and occupants of Isis-held areas all said they had evidence of fresh atrocities from the group. Isis has embraced a rule by terror since its militants took control of swaths of Iraq and Syria, committing and publicising massacres, attempted genocide of religious minorities and dissidents, widespread sexual enslavement, torture and child abuse.

The latest killings seem mostly targeted at former members of the security forces who Isis suspects might rise up against it, suspected resistance fighters or civilians who resist orders.

The group had allowed some members of the police to “repent” of their former allegiance and hand in their weapons when it took control, but its commanders are now said to be on high alert for plots.

In the town of Tel Keyf, dozens of former police officers were arrested and taken away two days before the push for Mosul began, said Ibrahim Ghazi, an officer in the Patriotic Union of Kurdistan party who iscollecting intelligence from Isis-controlled areas.

“Daesh [Isis] took 90 former police officers to Mosul and no one to this day knows what has happened to them,” Ghazi said. “These former officers were the ones who repented when Daesh took their town and, in return, they were spared.”

The UN’s human rights spokesman reported the killing of 50 former police officers in a building outside Mosul on Sunday, although he did not provide further details so it was not clear if they included some of the Tel Keyf officers.



He said Iraqi security forces discovered the bodies of 70 civilians last Thursday in houses in the village of Tuloul Naser, which lies south of the city, and had reports that 15 civilians were killed and their bodies thrown into the river in another village.

“We very much fear that these will not be the last such reports we receive of such barbaric acts,” said the UN spokesman, Rupert Colville.

Colville said the new allegations and information had come from civilians and established sources in northern Iraq that the UN had used in the past, who could not be named for their own security.

In another atrocity, Isis fighters reportedly shot dead three women and three girls who were lagging behind a group of civilians whom the terror group was moving to the city. The women and children were delayed because one of the girls, who was subsequently shot, was disabled.

Civilian casualties have been a concern for aid and rights groups since planning began for the battle of Mosul, which began last week after months of preparation.

As many as a million civilians still live in the city and its environs and humanitarian officials expect tens of thousands to flee in the first few weeks of fighting.

The battle pits up to 6,000 Isis fighters dug in around Mosul against 30,000 troops from a broad coalition including the Kurdish peshmerga, the Iraqi army and special forces, Shia militias allied with Iran, US warplanes and military advisers, and Turkish forces positioned to the north of the city.

Crowds rush to grab humanitarian packages, as smoke rises from a burning oil refinery in Qayyarah, south of Mosul. Photograph: Zohra Bensemra/Reuters

Human rights officials believe Isis is moving residents into the city to use them as human shields as the noose tightens around Mosul and the killings are designed to discourage locals from rising up against the group.

Commanders recently killed dozens of senior fighters for planning a rebellion, and Isis is likely to be suspicious of former security officials with weapons training.

A man who recently escaped Hamam Ali, south of Mosul, said a relative told him 200 men, mostly former police officers, had been killed by Isis as the Iraqi army closed in. “These officers were the ones who repented in the past and handed over their pistols, or if they didn’t have them paid a $2,000 fine,” said the man, who asked not to be named to protect his relative.

He said six men from a nearby village of Bab al-Tob were also executed after refusing to evacuate when the army attacked. “They were taken away by Isis, then shot dead.”

The killings were in line with past atrocities carried out by the group in its rampage across the Nineveh plains of northern Iraq, famous for their religious diversity. It evicted the vast majority of the area’s Christian population and launched a campaign of genocide against the Yazidi community, capturing thousands of women and girls who were then sold into sexual slavery.

Displaced people from the Yazidi community walk towards the Syrian border on the outskirts of Sinjar mountain. Photograph: Rodi Said/Reuters

When it captured Saddam Hussein’s hometown of Tikrit, the group carried out a mass slaughter of up to 1,600 Shia army cadets in its single worst atrocity of the wars in Syria and Iraq. Isis also destroyed many shrines and heritage sites.

More evidence of crimes is likely to be unearthed as the self-proclaimed caliphate recedes into the desert. Several mass graves were uncovered in the Yazidi homeland of Sinjar when it was recovered from Isis earlier this year.

Concerns have also mounted over possible abuses or revenge killings of suspected Isis members by the militias taking part in the campaign. The Shia militias in particular have been implicated in a range of violations such as forced disappearances and displacement after defeating Isis.

Combat inside the densely populated urban centre of Mosul will be particularly challenging, since the militants have had more than two years to prepare for an assault.

So far, at least 5,000 people have been displaced from Mosul’s outskirts amid the ongoing operation, including hundreds who fled to poorly equipped camps in Syria. Refugee camps near Mosul that have already been prepared can house up to 60,000 people.

“People who have fled from surrounding villages and towns tell us they’ve been driven to despair, waiting long days and weeks of hunger before they could flee to safety,” said Wolfgang Gressman, the Norwegian Refugee Council’s chief in Iraq. “Once again we call on the warring parties to put the safety and protection of Iraqi civilians as their top priority. This long, protracted nightmare has to stop.”