The Islamic State (IS) has killed 1,878 people in Syria over the past six months, the British-based Syrian Observatory for Human Rights reported Sunday.
The terrorist organisation has largely targeted civilians in their attacks, with only 703 of those killed being oppositional forces.
IS executed 502 Syrian soldiers and 81 insurgents, as well as 120 of their own members. According to the observatory, most of those killed were foreigners who wished to flee the organisation.
Observatory head Rami Abdulrahman reported that 116 of the militants killed were executed in the Syrian provinces of Deir Al-Zor, Raqqa and Hassakeh in the past two months. Four IS members were executed for other reasons.
Hundreds of IS militants are being held captive by the Kurds in Sulaymaniyah, and face prison or even death for their crimes against religious minorities.
An anonymous security official explained that it is easy for IS to recruit young Muslim men as members.
"Understand that most are young and have no information," he told Fox News. "They are impressionable. They listen to the second-life paradise story, 72 virgins, rivers of wine, and [staying] young forever. That is all they know. Some regret their actions, some do not."
Of the 1,175 civilians killed, eight were women and four were children. Abdulrahman said that 930 of the civilians were members of the al-Sheitaat tribe of eastern Syria.
The Sunni Muslims battled IS this summer for control of two oilfields. About 700 tribe members were reported dead in just two weeks.
The observatory's figures only account for deaths in Syria at the hands of IS. Thousands more have been killed in Iraq by the Muslim extremists.
The terrorist group, led by Abu Bakr al Baghdadi, has increased in power substantially since the withdrawal of US troops from Iraq in December 2011.
IS controls the Iraqi cities of Mosul, Baiji, and Fallujah, as well as parts of Syria. The group has posted photos and videos showing Iraqi policeman and civilians being slaughtered, and several videos of American and British journalists being executed.