File Photo: militants of the Islamic State group hold up their weapons and wave its flags on their vehicles in a convoy to Iraq, in Raqqa, Syria. AP
The Wednesday night attack in the Abu Khashab area in Deir el-Zour province targeted the home of a former spokesman with the US backed Syrian Democratic Forces, according to the Britain-based Syrian Observatory for Human Rights and Euphrates Post news website.
Euphrates Post said the gunmen arrived on motorcycles and opened fire as the group was having an iftar, the fast-breaking meal during the Muslim holy month of Ramadan at the home of former SDF spokesman Nouri Hameesh, who was among those killed.
Three years after IS lost the last sliver of territory it controlled, its sleeper cells have been increasing attacks in recent months, mainly targeting the Kurdish-led SDF but also forces from the Syrian government.
The Islamic State group's self-styled caliphate at its height covered a third of both of Iraq and Syria. The ensuing war against them lasted several years, killed thousands, and left large parts of the two neighboring countries in ruins.