The Syrian army’s own central command and control centre no longer functioned well after the Iranian and Hezbollah officers left.

The conflict's sectarian edge was hardened by the arrival of Iranian-backed Shi'ite fighters from across the Middle East to support Assad.

The pace of events has stunned Arab capitals and raised fears of a new wave of regional instability.

Russia’s distraction and weakening support for the Assad government partly explains the opportunity seized by the HTS and SNA coalitions.

Opposition sources in touch with Turkish intelligence said Turkey, which supports the rebels, had given a green light to the offensive.