The eastwards advance in an area south of al-Bab has extended Syrian army control across 14 villages and brought it within 25km (15 miles) of Lake Assad, the stretch of the Euphrates above the Tabqa dam.
Daesh's holdings in northwest Syria have been eviscerated over recent months by successive advances by three different, rival forces: Syrian Kurdish groups backed by the United States, the Turkey-backed rebels, and the Syrian army.
By taking Daesh territory south of al-Bab, the army is preventing any possible move by Turkey and the militant groups it supports to expand southwards, and is moving closer to regaining control of water supplies for Aleppo.
Fighting in the area is continuing as the army and its allies advance, the so-called Syrian Observatory for Human Rights, a Britain-based activist group, said on Sunday, Reuters reported.
Daesh's loss of al-Bab after weeks of bitter street fighting marks the group's effective departure from northwest Syria, once one of its most fearsome strongholds, and an area of importance because of its location on the Turkish border.