Peter Kassig
Colleagues of U.S. aid worker Peter Kassig (in the center picture), aka Abdul-Rahman Kassig, carry signs during a news conference calling for his release in Tripoli, Lebanon, Nov. 8, 2014. A video published online Sunday purports to show Kassig being killed by Islamic State militants. Reuters

The Islamic State group showed the severed head of U.S. aid worker Peter Kassig in one its most terrifying video releases yet. But the most gruesome scenes in the video, a 15-minute production appearing to be a recruitment effort that was released on Sunday, actually show the beheadings of 16 captured Syrian military servicemen. Just hours later, the group reportedly executed 18 Syrian civilians in its stronghold Raqqa.

Since the group also known as ISIS declared its caliphate in early June, it has killed nearly 1,500 Syrians, according to the Syrian Observatory for Human Rights. About a third were soldiers. "Four hundred eighty-three were regime soldiers, while four others were IS members,” SOHR director Rami Abdul Rahman told Agence France-Presse.

ISIS shows no qualms about displaying its brutality in gruesome detail when dealing with Syrian soldiers, unlike the videos featuring Western hostages, where the actual beheading is not shown. The soldiers were executed in retaliation for the Syrian president Bashar Assad’s crimes. The video released on Sunday opens with several scenes from regime attacks in Syria showing footage of injured children and Syrian hospitals. The narrator warns that ISIS will not forget the mass casualties from last year’s chemical attack in Ghouta, or the mass executions in Baniyas and Bayda. Those three massacres killed more than a thousand people, nearly all of them civilians.

But Assad isn’t the only one killing Syrian civilians. ISIS killed nearly 900 Syrian civilians since June, most of them from the Sunni Shaitat tribe, according to SOHR via AFP. The 18 executed Sunday were killed for being regime informants, according to the anti-militant activist group Raqqa Is Being Slaughtered Silently. After the men were shot, their bodies were left on the ground in a market square. The video that the activist group used as proof of this execution is too gruesome for International Business Times to display.

Besides shooting, ISIS is known for employing beheading as an execution method, after which the group tends to leave the bodies displayed in town centers as a deterrent, often crucified.

After ISIS beheaded and crucified one of its own members in Deir Ezzor recently, the body stayed on display for days. A photograph of the body was disseminated to ISIS followers and activist groups online.

“Don’t forget this is our daily life,” an activist from Deir Ezzor who goes by the name Abdul Hamid told IBTimes after seeing the photo. “Heads everywhere.”