AMMAN: An assassination operation that reportedly picked off five Islamic State fighters near the Euphrates Dam was most likely carried out by disaffected IS members, four rebel commanders and journalists told Syria Direct Wednesday.

Sunday night’s assassinations took place in “a closed-off, well-fortified location, which suggests that it was carried out by Islamic State members,” Abu Iskander, a commander with a rebel brigade fighting IS in the Aleppo countryside, who is originally from Raqqa, told Syria Direct Wednesday.

Furat al-Wafaa, an independent journalist formerly with the Raqqa is Being Slaughtered Silently campaign who is currently in the province's countryside, agreed: “An armed group sneaking into the area where the assassinations occurred is almost impossible.”

“If that is indeed the case, it represents a big development in the operations against the Islamic State inside Raqqa,” he added.

Five IS fighters were killed in Sunday's operation, including one non-Syrian, Husam Isa, a journalist with Raqqa is Being Slaughtered Silently told Syria Direct Wednesday. In the aftermath of the attack, the Islamic State executed a civilian and a member of its own Islamic Police (a-Shurta al-Islamiya) in the nearby town of Tabqa, reported pro-opposition al-Etihad Press.

“As tends to happen after every assassination operation, IS closed off everything in the area and is trying to prevent anyone from getting to the location,” said Isa. The site of the attack, the Euphrates Dam, is located just north of Tabqa city, which falls approximately 40km west of Raqqa.

A spokesman for Liwa Thuwwar Raqqa, the only major opposition group considered to have serious designs on Raqqa city, agreed that the assassination was likely carried out by IS members. Anti-IS sleeper cell activity in Raqqa is “very light, ” said Abu Muadh A-Raqqawi, connecting the the event to what he described as “differences within Islamic State ranks.”

“IS's repeated setbacks on the battlefield, and the differences within their ranks, especially between local and foreign fighters, proves the existence of internal assassination attempts,” the spokesman added.

“Most of the new IS fighters don't join because they love the group," said rebel commander Abu Iskander.

"They can't find work to provide for their needs.”