Bodies of one group believed to have been thrown into river in attempt to spread fear
Islamic State fighters are believed to have massacred scores of people around Mosul in the past week, the UN human rights office has said.
The group killed 50 police officers who were captured and held outside the city, according to sources in the area cited by UN human rights spokesman Rupert Colville.
And on Thursday, Iraqi security forces discovered the bodies of 70 civilians in houses in a village south of Mosul, Tuloul Naser.
"The bodies had bullet wounds, but it is not known for sure at this point who was responsible for the killings," Mr Colville told journalists in Geneva, Switzerland.
In Safina village, about 45km (30m) south of Mosul, 15 civilians were killed and their bodies thrown into the river in an attempt to spread fear.
Six men, apparently relatives of a tribal leader fighting against IS, were tied to a vehicle and dragged around the village.
"The six men were also allegedly beaten with sticks and gun butts. It is not clear what happened to them subsequently," Mr Colville said.
IS fighters have also reportedly shot dead three women and three girls, and wounded four other children, allegedly because they were lagging behind during a forced relocation from a village.
"The victims were lagging behind because one of the children had a disability. She was apparently amongst those shot and killed," he said.
Mr Colville also said officials kept receiving information that IS is "deliberately using civilians as human shields, forcing them to move to sites where ISIL (another name for IS) fighters are based, or preventing them from leaving other places for strategic reasons".
IS is battling US-backed Iraqi and Kurdish forces advancing on Mosul, the country's second-largest city and the militants' last urban stronghold in Iraq.
The offensive started last week.
Days ago, IS launched a surprise assault in and around Kirkuk, a Kurdish-controlled northern city some 170km (100m) southeast of the front lines of Mosul.
The UN said it was concerned about evictions of hundreds of displaced people in Kirkuk.
It could "significantly complicate the already alarming situation of mass displacement in the region", said Mr Colville.
Separately, the UN has voiced concern that Kurdish authorities had forced 250 displaced Sunni Arab families to leave Kirkuk, in a move called "collective punishment".
IS has also launched an attack in the town of Rutba in western Iraq.