According to the Syrian Observatory for Human Rights, the 15 military commanders were killed in a countryside near Raqqa for 'espionage and corruption on Earth' and 'impersonating al-Hisba (ISIS religious police) members'.
It comes as another monitoring group today said a leader of an al-Qaeda faction in Syria has also been killed in a U.S. air strike in Idlib.
According to the SITE Intelligence Group, Abu Firas al-Souri, a spokesman for the Nusra Front, was killed along with his son and several other people.
ISIS has suffered major defeats in Syria over the past months amid intense airstrikes by Russian warplanes.
Source: UK Mirror