Syria's official news agency SANA quoted a military source as saying the bus was hit overnight on a desert road in the Deir Ezzor province, noting that the terrorist attack has left a number of casualties.
The so-called Syrian Observatory for Human Rights, however, reported that the attack has claimed the lives of 26 troops and left 11 others injured, some in critical condition.
The terrorists surrounded the bus in the desert near Mayadeen and opened fire, the observatory added.
ISIL members in recent weeks have increased their surprise attacks in Syria's north and northeast, where they maintain hideouts.
The group, which seized wide swathes of Syria and neighboring Iraq in 2013, went underground since it lost its last territory in eastern Syria in 2019.
The attack was claimed by the ISIL later that day. They said they had carried out an ambush on "two military buses" and attacked them with "heavy weapons and rocket-propelled grenades." They also said they had set one of the buses on fire, according to a statement they released through their Amaq news agency.
Last week, the ISIL announced the death of its leader Abu al-Hussein al-Husseini al-Qurashi, who it said was killed in clashes in northwestern Syria. The group named Abu Hafs al-Hashimi al-Qurashi its new leader.
Last month, it claimed responsibility for the two bombings that hit the Sayyeda Zeinab area south of Damascus, killing and wounding dozens.
MNa/PressTV