The head of the Britain-based Observatory, Rami Abdel Rahman, said the air strikes were carried out by the US-led coalition.
“Twenty-five civilians, including seven children, were killed in the village of al-Shaafah and in surrounding desert areas in coalition strikes all through Sunday,” he said.
“This village is in the last pocket controlled by IS in the east of Syria,” he said of al-Shaafah referring to ISIS, which lies on the eastern bank of the Euphrates River.
Air strikes against jihadists forces holding out in remote areas of Deir Ezzor province have killed dozens of civilians in recent weeks, many of them relatives of the fighters.
Coalition-backed Kurdish-led forces have been trying to flush out ISIS from the east bank of the Euphrates, while Russian-backed regime and allied forces are stationed west of the river.
Abdel Rahman could not say how many ISIS combatants were taken out by the latest wave of air strikes.
“IS now holds less than three percent of Syrian territory,” he said using another acronym for ISIS.
The self-styled “caliphate” ISIS proclaimed over swathes of Syria and Iraq in 2014 effectively died when anti-jihadist forces retook its de facto capital Raqa and other strongholds such as Albu Kamal late last year.
However, the US-led coalition has continued to carry out strikes against small pockets of ISIS fighters hunkering down in and around small villages in Deir Ezzor province.
Small groups of ISIS-affiliated fighters are also still active in other parts of Syria.