Turkey says it has killed 25 "terrorists" in Syria, shortly after a monitoring group reported dozens of deaths on the fifth day of a Turkish military offensive against the Islamic State of Iraq and the Levant (ISIL) group and Kurdish forces in northern Syria.

The Syrian Observatory for Human Rights said at least 20 civilians were killed and 25 wounded near al-Amarneh, while 20 people died in Jeb al-Kussa, outside Jarablus, on Sunday.

The village of al-Amarneh was captured by Turkish-backed Syrian rebels from Kurdish fighters as part of the military offensive. Jeb el-Kussa is located 14km south of Jarablus and is controlled by fighters from the area backed by Kurdish forces.

The monitor also said at least four Kurdish fighters had been killed and 15 injured in Turkish bombardment of the two areas.

Citing military sources, however, Turkey's state-run Anadolu Agency said a total of 25 fighters of the outlawed Kurdistan Workers' Party (PKK) and the Syrian Kurdish People's Protection Units (YPG) were "neutralised" in an air operation in Syria.