In a communique Sunday, the non-governmental organisation revealed that the toll could be greater, given that there are unconfirmed reports that 26 more militants died in the same location.
The attacks took place overnight in the Al Tabani zone located in the western part of Deir el Zur province, which is almost entirely in the hands of the extremists.
The airstrikes by Syrian jets on the training camp also killed one child who was visiting a relative there.
The IS in late June proclaimed a Muslim “caliphate” in parts of Iraq and Syria, where it has taken over large swathes of territory.
The US is building an international coalition to fight the terrorist group both in Iraq, where Washington has already carried out dozens of airstrikes against IS positions, as well as in Syria.
Despite the military pressure, the IS is continuing to implement its policy of terror and during the weekend released a third videotape showing one of its black-clad fighters beheading another Western hostage – this time British social worker David Haines – with a knife.