In a recording posted online, Abu Huzaifa al-Ansari said IS members in Syria must fight "the new Syrian regime, with its secular government and national army" and "make that their priority."

Since ousting longtime rule Bashar al-Assad in December 2024, Syria's new authorities, who had links to the Al-Qaeda jihadist group, have sought to break from their radical past and present a moderate image.

Last year, Syria joined the US-led coalition against IS and has been coordinating attacks against the group's remnants in the country.

IS swept across Syria and Iraq in 2014, committing massacres and forcing women and girls into sexual slavery.

Backed by US-led forces, Iraq proclaimed the defeat of IS in 2017, followed two years later by Kurdish-led forces in Syria.

Last month, Syrian troops advanced against Kurdish forces, sparking questions over the fate of the IS prisoners held in Kurdish-led facilities.

Amid lingering doubts about security, Washington transferred more than 5,700 IS detainees from Syria to Iraqi prisons.

A camp that once held relatives of IS fighters has now been emptied -- residents either left or were moved to a new location by the Syrian authorities.