An air strike by the US-led coalition has killed the founder of the Islamic State propaganda media outlet Amaq in the eastern Syrian province of Deir al-Zor, his brother said in a Facebook post on Wednesday.

Reuters could not independently confirm whether he had been killed. There was no immediate comment from the United States-led coalition against Islamic State.

The post said the strike killed Rayan Meshaal and his daughter in their home in the city of al-Mayadin. Syrian opposition activists had been sharing news of Meshaal's death on social media.

"I'm pleased to announce the martyrdom of my older brother Baraa Kadek, known as Rayan Meshaal...in an air strike by the coalition," the Facebook post reportedly by his brother said.

Islamic State often claims responsibility for attacks worldwide through Amaq channels on social media.