A US-backed force and two Syrian activist groups say ISIS militants have carried out an attack in the city of Raqqa in northern Syria.

Axar.az reports citing Alarabiya that the early Wednesday attack targeted a post of the US-backed Kurdish-led Syrian Democratic Forces in Raqqa, which was once the extremists’ de facto capital.

The attack comes as Turkey is expected to launch an offensive against the Kurdish fighters in northeastern Syria.

The Kurdish fighters say ISIS launched three suicide attacks against its positions in Raqqa. There was no word on casualties.

Raqqa is being Silently Slaughtered, an activist collective, reported an exchange of fire and a blast.

The Britain-based Syrian Observatory for Human Rights, a war monitoring group, says the attack involved two ISIS fighters who engaged in a shootout before blowing themselves up.