An "Islamic State of Iraq and Syria" (ISIS) suicide bomber attacked a centre for Kurdish forces in the northern Syrian city of al-Raqa on Monday (January 7th), killing four civilians and an anti-ISIS fighter, AFP reported.

The attacker blew himself up after entering the centre run by the Kurdish People's Protection Units (YPG), the Syrian Observatory for Human Rights said.

"A suicide attacker wearing an explosives belt blew himself up inside a YPG centre after opening fire on a security checkpoint at its entrance," Observatory chief Rami Abdel Rahman said.

At least four civilians and a YPG fighter were killed in the attack, he added.

The YPG forms the backbone of the Syrian Democratic Forces (SDF), an Arab-Kurd alliance battling to expel ISIS from its last redoubt in eastern Syria.

ISIS claimed responsibility for the attack in a statement on the Telegram messaging app.

Backed by the international coalition, the SDF has in recent weeks advanced against ISIS in its last holdout in the eastern province of Deir Ezzor.