BEIRUT (AP) — Syrian activists say a bomb blast in a northern town held by Turkish-backed opposition forces has killed at least eight people.

The explosion on Sunday in Afrin is the latest in a series of attacks in areas held by Turkish troops and their Syrian allies, who have seized a swath of territory along the border from Islamic State militants and Kurdish fighters.

Turkey has vowed to expand the offensive to root out Syrian Kurdish fighters, who joined with the U.S.-led coalition to drive out IS. Turkey views the Kurdish fighters as an extension of the insurgency within its borders.

The Syrian Observatory for Human Rights says the market explosion on Sunday killed eight people. The activist-run Shaam news agency says a blast in Afrin on Thursday killed three.