, rights groups have said.
Evidence gathered by Amnesty International researchers in al-Shura and al-Qayyara districts indicates that six people were shot dead on suspicion of having ties to the militants, a report from the group said on Thursday, and several more detained and beaten.
The claims are the first reported abuses of cilviians' human rights by Iraqi forces in the battle to date.
The four-week-old offensive to retake Mosul has driven Isis to retreat from surrounding towns and villages, in many cases taking hundreds of civilians with them as human shields.
Ten men and a 16-year-old boy who escaped being forcibly moved in late October handed themselves over to men wearing police uniforms, Amnesty found. Some had waved white cloth and pulled up their shirts to show they were not wearing explosive vests.
Six were handcuffed on the presumption they were Isis fighters who had been left behind and taken to an open desert area where they were insulted with sectarian language and beaten with rifle butts, punched and kicked. They were made to lie on their stomachs while shots were fired between their legs, Amnesty said, before three men were separated from the group and shot.
In pictures: Mosul offensive
Three more men in the area were also killed in separate incidents after trying to hand themselves over to men in police uniforms.
“When the Mosul military operation began, Prime Minister Haider al-Abadi made clear that violations by Iraqi armed forces and its allies would not be tolerated. Now is the time for him to prove just that,” Lynn Maalouf, deputy director for research for Amnesty in Beirut said.
“The Iraqi authorities must immediately investigate these alarming reports of extrajudicial executions and torture,” she added.
A statement from the Command of the Federal Police Forces denied the claims, saying that all pro-government forces in the coalition offensive to retake the city of Mosul were committed to protecting civilian lives and property.
It is not the first time Amnesty has documented supposed extrajudicial executions by men wearing Iraqi police uniforms in the fight against Isis: the group said that 16 men and boys were killed in similar circumstances after handing themselves over to liberating forces in the battle for Fallujah in May.
“Without effective measures to suppress and punish serious violations, there is a real risk that we could see war crimes of this kind repeated in other Iraqi villages and towns during the Mosul offensive,” Ms Maalouf added.
Isis has also reportedly been tricking civilians by wearing Iraqi army fatigues and posing as Iraqi coalition forces: when residents go out to greet them they were shot, said Tariq, an engineering student from Hammam al-Alil, which was recaptured by pro-government forces last week. “Even a one-year-old baby, they put a bullet in his head,” he said.
The US-backed Operation Inherent Resolve to retake Mosul - Iraq’s second largest city and home to at least 1.5million people - began last month, aimed at ousting Isis after two years and ending the group’s incarnation as a land-holding force in Iraq.
Units from the 30,000 strong coalition of Kurdish Peshmerga, Iraqi army and Sunni and Shiite militias has entered Mosul’s suburbs from the east, where they have been met with fierce resistance from jihadis in the form of suicide bombers, snipers and boobytrapped roads and bridges, and are preparing a second assault on the city from the south.