23 Syrian soldiers killed in attack on military bus

The attack occurred near the town of al-Mayadeen in the vast desert province of Deir Ezzor, where control is divided between Syrian troops backed by Iran and Russia and Kurdish groups backed by the United States.

SOHR described it as the deadliest attack by the Islamic State this year. After seizing large swathes of territory in Syria and neighboring Iraq since 2013, the group went underground in 2019 after losing the last of its territory in eastern Syria.

Syrian state media did not report on the incident and no one has claimed responsibility for the attack.

Attacks by Islamic State sleeper cells in Syria, particularly in the vast desert areas they once controlled, have become bolder and bloodier in recent months, according to SOHR's Rami Abdel Abdel Rahman.

This month, the Islamic State announced Abu Hafs al-Hashimi al-Quraishi as its new leader and confirmed for the first time the death of its former leader, Abu Hussein al-Husseini al-Quraishi, whom Turkey said it killed in April.