ISIS leader Abu Bakr Al Baghdadi's son, Hudhayfah Al Badri, was killed during an attack in the central Syrian province of Homs, ISIS propaganda agency Amaq said on Tuesday.
Al Badri was killed in an "operation against the Nussayriyyah and the Russians at the thermal power station in Homs", the extremist group said.
ISIS uses the term Nussayriyyah for the Alawite religious minority sect of President Bashar Al Assad.
In 2014, the group announced a "caliphate" in Syria and Iraq, seizing a third of Iraq during a sweeping offensive. Since then, ISIS has lost ground to separate counter-offensives by Syrian and Iraqi forces as well as US-led operations. The extremists are estimated to control no more than 3 per cent of Syria's territory.
Last December, the Iraqi government declared victory over ISIS but the military has continued regular operations targeting mostly desert areas along the porous Syrian border.
Al Baghdadi, who has been pronounced dead on several occasions, remains alive in Syrian territory by the Iraqi border, an Iraqi intelligence official said in May. He was said to move around with only a small group of followers
Al Baghdadi, from Iraq, has been dubbed the "most wanted man on the planet" and the US is offering a $25 million (Dh91.8m) reward for his capture.
The Iraqi official said the noose was closing around the extremist leader after Iraqi forces captured five top ISIS commanders in an unprecedented raid in Syria on March 24.
Last September, in the last voice message attributed to Al Baghdadi, the ISIS leader called on his fighters in Syria and Iraq to "resist" their enemies.