The Islamic State of Iraq and the Levant group has been committing a wave of atrocities around the Iraqi town of Mosul, according to the reports received by the United Nations, as Iraqi troops close in to capture the ISIL stronghold.
The allegations, which remain "preliminary", have come from a range of civilian and government sources, who cannot be named for security reasons, the UN rights office spokesman Rupert Colville said on Tuesday.
The reported atrocities were perpetrated by ISIL members between Wednesday and Sunday, while tens of thousands of Iraqi forces advanced towards Mosul, the last ISIL bastion in the country, Colville said.
In a village called Safina, about 45km south of Mosul, ISIL (also known as ISIS) was blamed for executing 15 civilians before throwing their bodies in a river, possibly to strike terror among other residents.
On October 19 also in Safina, fighters "reportedly tied six civilians to a vehicle by their hands and dragged them around the village, apparently simply because they were related to a particular tribal leader fighting against ISIL," Colville said.
Iraqi security forces reportedly found another 70 bodies riddled with bullet wounds on October 20 in the nearby Tuloul Naser village. Colville said it was not immediately clear who was responsible for their deaths.
In addition, on Saturday, ISIL gunmen allegedly shot dead three women and three girls during a forced march in Rufeila village south of Mosul, according to the rights office spokesman.
The 50 police officers who had been held hostage by ISIL were reportedly killed in a building outside Mosul on Sunday, Colville also told reporters in Geneva.
"We very much fear that these will not be the last such reports we receive of such barbaric acts by ISIL," he said.
He added that all the allegations "need a bit more [investigative] work" before the UN can conclusively say they took place.
The rights office also restated its fears that ISIL will use civilians in Mosul as human shields as Iraqi forces fight to retake the city in an operation backed by a US-led coalition.
The campaign to retake Mosul comes after months of planning and involves more than 25,000 Iraqi troops, Kurdish forces, Sunni tribal fighters and state-sanctioned Shia militias.
It is expected to take weeks, if not months, to drive ISIL out of Iraq's second largest city, which is still home to more than a million people.
ISIL has suffered a series of setbacks over the past year, and Mosul is its last major urban bastion in Iraq.