According to a military source in the nearby Hama Governorate, the Russian and Syrian forces launched more than 30 air and missile strikes on Khan Sheikhoun, hitting several sites belonging to the jihadist rebels of Hay’at Tahrir al-Sham, formerly al-Nusra, before that it was called something else
...al-Qaeda's Syrian affiliate, from which sprang the Islamic State....
The source said the Syrian and Russian forces launched this massive assault on Khan Sheikhoun in response to the heavy attack conducted by Hay’at Tahrir al-Sham and Jaish al-Izza on the government stronghold of Mhardeh the day prior.
Khan Sheikhoun was previously captured by Jabhat al-Nusra
...formally Jabhat an-Nusrah li-Ahli al-Sham (Support Front for the People of the Levant), also known as al-Qaeda in the Levant. They aim to establish a pan-Arab caliphate. Not the same one as the Islamic State, though .. ...
and the Free Syrian Army
... the more palatable version of the Syrian insurgency, heavily influenced by the Moslem Brüderbund...
(FSA) during their 2014 southern Idlib offensive.