The militant group itself has not reported the death of the founder of Aamaq news agency, Baraa Kadek.
But his brother, Hozaifa, posted on his Facebook that Kadek and his young daughter were killed in an airstrike in Mayadeen town in Deir el-Zour province.
Other Syrian opposition news outlets, including Halab News Network and Qasioun news agency, reported Kadek's death late yesterday. But it was not immediately clear where Kadek was killed or when. His brother said he was killed in his home.
There was no immediate comment from the coalition. Last week, the coalition told The Associated Press it had carried out a series of airstrikes on May 25 and 26 targeting IS media infrastructure and "propaganda facilities." It said at the time that targeting such facilities "degrades" the group's abilities and inspiration of foreign attacks.
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Aamaq news agency has become the group's fastest and most reliable source of information, using it to post videos and claims of attacks. It has remained online despite bans from social media platforms.
Kadek became known as a media activist covering the outbreak of protests in 2011 then rebel fronts. Originally from Aleppo province, he later joined IS in 2013 and set up the group's flagship media arm.