Beirut - At least 35 Syrian soldiers and pro-regime militiamen were killed on Saturday in a multi-front attack by the Islamic State group (ISIS) on the eastern city of Deir Ezzor, a monitor said.
The Syrian Observatory for Human Rights said the jihadist group had advanced into the northern tip of the city and captured the suburb of Al-Baghaliyeh.
The advance puts ISIS in control of around 60% of Deir Ezzor, with the regime holding the rest, according to the Britain-based monitor.
Syrian state news agency SANA said regime troops had repelled an ISIS attack on the area around Al-Baghaliyeh and inflicted "heavy losses" on the group.
Deir Ezzor is the capital of Deir Ezzor province, an oil-rich region that borders Iraq and is mostly held by ISIS.
The regime has clung onto portions of the provincial capital and the adjacent military airport despite repeated ISIS attacks.
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.
Eight of the regime forces killed were shot dead in executions by ISIS, the Observatory added.
The group said Russian warplanes were carrying out heavy air strikes in support of regime forces as they sought to repel the ISIS advance.