U.N. officials call the figures "staggering," but say the situation may actually be much worse. The figures are based on information from survivors and witnesses, but many atrocities could not be documented.
U.N. spokeswoman Ravina Shamdasani said, "ISIL [an acronym for the militant group] in particular has been employing the most gruesome methods to execute people; by running bulldozers over them, by burning them alive. In one case, people were put in a cage and the cage was then thrown into the water.
"People are being murdered for the most obscure of reasons. One imam was killed because he was not praying correctly. There are children that have been abducted by ISIL. We have documented about 800 children who were abducted and then forced to fight, put in religious schools or sent directly to the front lines," Shamdasani said.
Violence does not necessarily stop once an area is reclaimed from Islamic State.
"We have also documented violations by pro-government forces. In some cases, when people flee ISIL-occupied areas they are then arrested by security forces or they are expelled," she said.
The United States could not immediately confirm the death toll from the report, but a State Department spokesman Tuesday said Islamic State atrocities are well-known.
U.S. State Department spokesman John Kirby said, "The depth of ISIL's depravity has already been well documented, and this report continues to show the horrendous methods that ISIL has used in its campaign of terror."
Japan announced plans Tuesday to send additional aid to help refugees fleeing violence in Iraq and Syria.
Japanese Foreign Minister Fumio Kishida said, "In addition to the aid worth $810 million that we have dispersed for refugees and internally displaced people in Syria and Iraq, and for neighboring countries, I would like to announce a plan to provide additional aid of $350 million, pending the approval of the necessary budget."
Thousands of others fleeing violence in Iraq, Syria and elsewhere are now without shelter in the freezing temperatures as they cross the Balkan countries on the way to Western Europe.