The Observatory said "dozens of (other) soldiers" were missing.
At least 23 Syrian soldiers have been killed in the conflict-torn country's east in an attack on an army bus blamed on Islamic State group jihadists, a monitor said Friday.
IS "members targeted a military bus" in Deir Ezzor province on Thursday, said the Syrian Observatory for Human Rights, as remnants of the jihadist group escalate their attacks.
The attack killed "23 soldiers and wounded more than 10 others", some of whom in critical condition, said the Britain-based group which relies on a wide network of sources inside Syria.
The Observatory said "dozens of (other) soldiers" were missing.
Despite losing their last piece of territory in Syria in 2019, IS has maintained hideouts in the vast Syrian desert from which it has carried out ambushes and hit-and-run attacks.
Its members in recent weeks have increased their attacks in Syria's north and northeast.
Ten Syrian soldiers and pro-government fighters were killed earlier this week in an IS attack in the former jihadist stronghold of Raqa province, the Observatory said Tuesday.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)