At least one civilian was killed and three others injured Friday in a mortar attack by the PKK terrorist group's Syrian affiliate the People's Protection Units (YPG) in northern Aleppo province, according to local sources.

The mortar attack targeted civilians in Syrian's town of Marea which is mostly populated by civilians, said the sources, speaking on condition of anonymity due to restrictions on speaking to the media.

Three civilians who were injured during the attack were taken to hospitals close to the region.

Syria has only just begun to emerge from a devastating conflict that began in 2011, when the Assad regime cracked down on demonstrators with unexpected ferocity.

The PKK -- listed as a terrorist organization by Turkey, the U.S. and the EU -- has waged a terror campaign against Turkey for more than 30 years, resulting in the deaths of nearly 40,000 people, including women and children.