DAMASCUS, Feb. 23 (Xinhua) -- An Islamic State (IS) attack killed four members of Syria's internal security forces at a checkpoint west of the northern city of Raqqa on Monday, a Syrian security source said.

The source told state news agency SANA that the attack targeted the Sabahiya checkpoint, without providing further details on how it was carried out or whether the assailants were captured or killed.

The incident underscores persistent security challenges in parts of northern Syria, where IS sleeper cells continue to stage sporadic raids despite the group's territorial defeat in 2019.

Raqqa, once the de facto capital of the IS self-declared caliphate, has seen periodic assaults on checkpoints, patrols, and local officials in recent years, particularly in rural areas surrounding the city.

The city came under the control of Syria's interim authorities earlier this year following the withdrawal of the Kurdish-led Syrian Democratic Forces under a broader security and administrative agreement aimed at reducing tensions in northern Syria.

Since then, government security units have deployed across Raqqa and its countryside as authorities seek to restore state institutions and prevent an IS resurgence in the vulnerable region.■