Since claiming to have established a caliphate in the Middle East last June, the extremists have carried out a huge number of sickening public executions - ranging from beheadings, shootings and stonings to crucifixions, beatings and being pushed from the roofs of high buildings.
According to the report, 74 children have been brutally murdered by ISIS since the terror group self-declared the establishment of a caliphate and claimed leader Abu Bakr al-Baghdadi was the head of the world`s Muslims during a sermon in Mosul`s grand mosque on June 29 last year.
Members of Sunni Shaitat tribe account for around half the civilians killed.
ISIS brutally executed 930 members of the clan in Deir Ezzor last year after they rose up against the extremist Sunni Muslim group.
The toll also includes recent mass killings by ISIS in the Syrian Kurdish town of Kobane, which the terror group re-entered briefly this week after being expelled in January.
The monitor said it had counted at least 223 executions in the Syrian border town this week.
The Observatory also documented 216 ISIS executions of rival rebel factions and Kurdish fighters, as well as the bloody killings of nearly 900 soldiers loyal to President Bashar al-Assad`s regime.
ISIS has also executed 143 of its own members it accused of crimes including spying - many of them captured as they were trying to desert the group, the Observatory said.
Meanwhile at least 8,000 jihadis have been killed in fighting and US-led air strikes in recent months.
ISIS emerged in Syria in 2013, growing from Al-Qaeda`s one-time Iraq affiliate and initially seeking to merge with Al-Qaeda`s Syrian affiliate Al-Nusra Front.
When Al-Nusra refused the merger, the two groups become rivals, and IS went on to announce its `caliphate` in territory in Syria and Iraq last year, proclaiming al-Baghdadi as `Caliph Ibrahim`.
The news comes as aid agencies warned that the number of Syrian children being forced to work keeps growing as the conflict drags on, with those as young as six reportedly working in Lebanon.
Syrian refugee children have become the joint or sole breadwinners in almost half of the households surveyed in Jordan, the United Nations Children`s Fund and Save the Children said in the first comprehensive report on child labour among Syrian children across the region.
`Based on all of these surveys...it`s clear that child labor has increased substantially since the Syrian conflict began,` UNICEF spokesperson Juliette Touma revealed.
Children keep being recruited as soldiers in the five-year-old conflict, they are being sexually exploited and trafficked according to the report, which draws on data collected in recent years.
The war in Syria has killed more than 220,000 people and displaced around half of the population. U.N. aid agencies have described it as one of the worst refugee crises since World War Two.
The conflict has pushed thousands of children into the labour force.
They now harvest potatoes in Lebanon, work in shops and restaurants in Jordan, bake bread and fix shoes in Turkey and are exposed to multiple hazards in quarries and construction sites.
Three out of four working children surveyed at the Zaatari refugee camp in Jordan said they suffered from health problems, according to the report.
The report said most children in host communities in Jordan work six or seven days a week earning between £2.50 and £4.50 daily.
