18 fighters killed in east Syria violence: Syrian Observatory for Human Rights
Russian air strikes on positions held by IS in desert areas of the Hama and Raqa provinces killed nine jihadists, the Syrian Observatory for Human Rights said.
The Britain-based war monitor said the death toll could rise since at least 22 others were wounded in the strikes, some of them seriously.
The latest of the 230 air raids carried out in Syria this year by Russia came after two IS attacks in the Deir Ezzor province killed nine fighters allied to the Kurdish security forces on Wednesday, the Observatory said.
The jihadist group's self-proclaimed "caliphate" was defeated in that same province three years ago but IS fighters have continued to harass the forces that now control the region.
The Kurdish forces leading the battle against IS in northeastern Syria are supported by Arab tribal fighters.
IS launched massive attack on a Kurdish-run prison last month. It is unclear how many inmates were sprung but more than 250 jihadists were killed in subsequent fighting.
A US special forces raid in northwestern Syria last week killed the organisation's leader, Abu Ibrahim al-Qurashi. IS has not yet acknowledged his death nor announced a successor.