Men wearing federal police uniforms tortured and executed civilians in villages south of Mosul during an ongoing operation to retake the city from ISIL, according to a rights group, an allegation denied by Iraq's authorities.
In a report published on Thursday, Amnesty International said its researchers had gathered evidence that up to six people were "extrajudicially executed" last month in the al-Shura and al-Qayyarah sub-districts over suspected ties to ISIL, also known as the Islamic State of Iraq and the Levant or ISIS.
Three of the victims were part of a group of around 10 men and one 16-year-old boy who handed themselves over to men wearing federal police uniforms on October 21, the rights group said.
The men had waved a white cloth and lifted their shirts to show they were not wearing explosive belts, Amnesty said, but were taken to an open desert area and brutally beaten. One man's beard was set alight.
On the same day, another victim was led away by men in police uniforms, only for his body to be found a week later, according to Amnesty, which said that its researchers had visited several villages in Shura and Qayyarah.
Again on October 21, another man was reportedly shot as he ran towards men in police uniform, pulling at his clothes to show he was not wearing a bomb.
And the body of a sixth man, who had defied ISIL's attempt to remove civilians for use as human shields and stayed in the Shura area, was found with bullet wounds to the chest and chin after government forces moved in, according to the UK-based rights group.
Amnesty said that forces operating in the area "were apparently presuming that only ISIL fighters had remained behind", but that the extrajudicial executions were in any case unlawful.
"Men in federal police uniform have carried out multiple unlawful killings, apprehending and then deliberately killing in cold blood residents in villages south of Mosul," said Lynn Maalouf, deputy director for research at Amnesty's Beirut office.
"Deliberately killing captives and other defenceless individuals is prohibited by international humanitarian law and is a war crime," she added.
In an interview with Al Jazeera, Maalouf also called Iraq's authorities to urgently conduct proper investigations.
"It is crucial at this point, as the operation is ongoing, and Iraqi authorities are effectively taking control of these areas, to ensure that trust is maintained in the civilian population, and one of the ways to do that is to investigate these kinds of reports."
Later on Thursday, Iraq's federal police issued a statement denying its forces had been involved in extrajudicial killings.
A spokesman for the federal police said that its officers respected the human values and principles of civilians and their property, as well as providing all possible assistance to them during the operation to retake Mosul.
The federal police had been providing humanitarian aid, he said, adding that its forces had managed to rescue and evacuate more than 10,000 families who were being held by ISIL fighters as human shields.
A spokesman for Iraq's interior ministry also denied there had been any violations and said Iraqi forces respect human rights and international law.
The Mosul operation, involving a 100,000-strong alliance of troops, security forces, Kurdish Peshmerga and Shia militias and backed by US-led coalition air strikes, has entered its fourth week but is facing fierce resistance for ISIL fighters.
As Iraqi forces struggle to solidify gains in neighbourhoods in eastern Mosul, more and more civilians are fleeing the city and its surrounding areas.
Also on Thursday, rights group Human Rights Watch (HRW) said at least 37 men suspected of being affiliated with ISIL had been detained by Iraqi and Kurdish forces from checkpoints, villages, screening centres and camps for displaced people around Mosul and Hawija, further south.
Relatives said they did not know where most of the men were being held and had not been able to contact any of them while in detention, according to HRW's report.
The group also warned that such conduct "significantly increases the risk of other violations", including torture.
A spokesman for the Kurdish regional government denied the HRW report, saying any delays in informing families were limited and due to limited resources.
"Nobody has been kept in unknown facilities. They are kept in identified facilities," Dindar Zebari told Reuters news agency.