Turkish President Recep Tayyip Erdogan has vowed that Turkey will show the same determination in fighting the Islamic State group and Syrian Kurdish fighters, on the fifth day of a cross-border operation that has already left dozens dead in northern Syria, Al Jazeera reports.

Speaking on Sunday, August 28 in Gaziantep in southeast Turkey, where 54 people were killed in a suicide attack at a Kurdish wedding last week, Erdogan said: "We cannot tolerate any terror organisation within or close to our borders.

"That's why we are in [Syria's] Jarablus. And, if necessary, we will not flinch from taking on similar responsibilities in other areas."

On Sunday, Turkey intensified its "Euphrates Shield" military offensive in northern Syria, with Turkish warplanes and artillery pounding areas held by pro-Kurdish forces close to Jarablus, the town taken from ISIL by Ankara-backed Syrian rebels earlier this week.

The UK-based Syrian Observatory for Human Rights said at least 40 civilians were killed in separate Turkish strikes near the village of al-Amarneh and in Jeb al-Kussa, outside Jarablus - the first reports of significant civilian casualties since the start of Turkey's operation on Wednesday.

The group, which monitors Syria's war, also said at least four Kurdish fighters had been killed and 15 wounded in the bombardments south of Jarablus.

But Turkey denied the reports of civilian deaths, saying its raids had killed 25 Kurdish "terrorists", according to the state-run Anadolu news agency.