A new report from Human Rights Watch says an Iraqi army division trained by American forces allegedly executed prisoners in west Mosul.
The latest report of executions comes after the release of videos allegedly shot in the Mosul area that appeared to show Iraqi forces executing one detainee and brutally beating others.
Iraq declared victory in Mosul on July 11, but abuses by security forces and the anger they stoke could pose a potentially major threat to long-term stability in an area that was only just recaptured from ISIS.
"An Iraqi army division trained by the United States government allegedly executed several dozen prisoners in Mosul's Old City," HRW said in a statement, referring to an area on its western side.
"Two international observers detailed the summary killings of four people by the Iraqi army's 16th Division in mid-July 2017, and saw evidence that the unit had executed many more people, including a boy," the watchdog said.
The international US-led coalition against ISIS has provided training, advice and other assistance to various Iraqi units.
"The US government should make sure it is no longer providing assistance to the Iraqi unit responsible for this spate of executions," Sarah Leah Whitson, HRW's Middle East director, said in the statement.
Earlier in July, HRW found a series of videos posted online that appeared to show other abuses by Iraqi forces in the Mosul area.
In one clip, men in Iraqi army uniforms beat a bearded detainee, drag him to the edge of a cliff, throw him off and shoot him and another body at the bottom.
Three other videos show men in army and police uniforms beating detainees.
Earlier in the Mosul operation, an Iraqi journalist embedded with the Rapid Response Division reported that members of the special forces unit carried out torture, rapes and killings.
The journalist, who has since left Iraq, documented some of the abuses on film.
ISIS overran Mosul and swathes of other territory in the summer of 2014, but Iraqi forces backed by US-led air strikes have since regained much of the territory they lost.
Widespread anger among Iraqi Sunni Arabs — over issues including abuses by security forces — helped aid the jihadist resurgence which culminated in the 2014 offensive.
Abuses by security forces now are likewise a boon to ISIS, which is thought likely to increasingly revert to bombings and hit-and-run attacks as its cross-border statehood project continues to fall apart.