At least 35 Syrian soldiers and pro-regime militiamen were killed Saturday in a multi-front attack by the Islamic State group on the eastern city of Deir Ezzor, a monitor said.
The fighting came as regime forces battled ISIS in the northern province of Aleppo, repelling a jihadist assault and killing at least 16 fighters from the group.
Observatory chief Rami Abdel Rahman said heavy fighting was continuing on Saturday afternoon after the ISIS assault, which began with a suicide car bomb blast carried out by a member of the jihadist group.
The monitor said Russian warplanes were carrying out heavy air strikes in support of regime forces as they sought to repel the jihadists.