An attack by ISIS in the Syrian desert Thursday killed 11 regime and allied fighters, the Syrian Observatory for Human Rights said.
The fighters died in an attack on their vehicle between Al-Sokhna and Al-Shula in the area straddling Homs and Deir Ezzor provinces.
Rami Abdel Rahman, the head of the UK-based monitor, warned that the casualty toll could rise.
There was no immediate claim from ISIS.
At least 27 regime and allied fighters were killed in an attack by the militant group in the same desert area on April 9.
ISIS has also carried out deadly attacks in Iraq in recent weeks.
Observers have warned that border closures and mobilization of security resources due to the coronavirus pandemic could give rise to a surge in ISIS attacks.
The extremist group no longer has fixed positions, but it still has hundreds of militants hunkered down in desert hideouts.
Two members of the Kurdish-led Syrian Democratic Forces were also killed in a suspected ISIS attack in Baghouz, near the border with Iraq, the Observatory said.
Such attacks against the SDF have been frequent in the Baghouz area.
