KARKAMIS - Turkish forces backed by tanks clashed with pro-Kurdish fighters in northern Syria Saturday as Ankara presses a four-day offensive aimed at driving both Islamic State (IS) jihadists and Kurdish militia from its border.

The clashes took place eight kilometres (five miles) south of the town of Jarabulus, the border town recaptured from IS this week by Turkish-backed Syrian rebels, a monitoring group and Kurdish sources said.

"Turkish tanks advanced today near Al-Amarneh in Aleppo province, south of the border, and clashes broke out between them and fighters backed by Kurdish forces," Syrian Observatory for Human Rights head Rami Abdel Rahman said.

A source within northern Syria's autonomous Kurdish region confirmed the clashes. There was no information on casualties.

The Kurdish-backed rebels said Turkey had carried out airstrikes on its positions.

"Turkish jets have this morning bombarded our positions in southern Jarabulus and the Al-Amarneh village," said the Jarabulus Military Council which is linked to the Kurdish-dominated Syrian Democratic Forces (SDF).

"With this aggression, a new conflict period will begin in the region," it said.

Turkey's state-run Anadolu agency reported that the army had carried out strikes against a weapons arsenal and command post belonging to "terror groups".  The agency did not say if the bombardment was from artillery or war planes or specify which groups were targeted.

The clashes suggest Turkey is ramping up its offensive inside Syria four days after it launched operation "Euphrates Shield" to counter both IS and the Kurdish People's Protection Units (YPG) militia.

On Thursday, Turkey had already shelled Syrian Kurdish targets near Jarabulus in what was seen as a warning to them to retreat.

On Saturday, an AFP correspondent at the Turkish border village of Karkamis saw six more tanks crossing into Syria, adding to the dozens of tanks and hundreds of troops already in the country.

Turkey fiercely opposes moves by the YPG to expand into territory lost by IS.

Ankara fears the emergence of a contiguous autonomous Kurdish region in Syria would bolster Kurdish rebels across the border in southeast Turkey.

Its campaign against the Kurdish fighters puts it at odds with NATO ally the US which supports the YPG as an effective fighting force against IS.

- 'Brink of starvation' -

On Saturday, the last rebel fighters were evacuated from Daraya just outside the Syrian capital Damascus, under a plan to end a brutal four-year siege of the town that brought the population to the brink of starvation.

Hundreds of fighters and their families were bused north into rebel-held territory in Idlib province.

"The Syrian army completely controls Daraya and has entered all of the town. There isn't a single armed man there," a Syrian military source told AFP.

The rebels said they were forced to give up the town, which was one of the first to rise up against the government, accusing Damascus of using "starve or surrender" tactics.

The roughly 8,000 civilians left in the town are also to be evacuated.

In Syria's northwest, fighting continued to rage between Syrian government forces and rebels in the battered city of Aleppo, in spite of tentative plans for a 48-hour ceasefire.

At least 15 civilians were killed in barrel bomb attacks by regime aircraft on the rebel-held Maadi district in the city's east, the Britain-based Syrian Observatory said.

An AFP reporter in the area confirmed the attack, saying the two bombs fell within minutes of each other.

The UN's Syria envoy Staffan de Mistura called on the warring parties in Aleppo to state by Sunday whether they will commit to a two-day humanitarian truce to allow in aid after weeks of fierce fighting that has left hundreds dead.

He voiced regret that some opposition forces were baulking at the plan, which has been endorsed by Russia, a staunch ally of the Syrian regime.

Russia and the US signalled progress towards a deal on a ceasefire at marathon talks in Geneva on Friday.

"Today I can say that we achieved clarity on the path forward" for a revamped cessation of hostilities, US Secretary of State John Kerry said.

His Russian counterpart Sergei Lavrov added that "very important steps" had been made on a deal to stop the violence.

Russia, a staunch ally of Assad's regime, has been backing government forces with air strikes on rebel-held areas.

The US supports Syria's main opposition alliance and some other rebel factions.

- Demining -

Turkey's offensive in Syria adds yet another layer to the tangled web of powers jockeying for influence in the country.

Ankara says that the Kurdish YPG militia has failed to stick to a promise to return across the Euphrates river after advancing west this month.

On Saturday, Turkish-backed rebels continued clean-up operations in the town of Jarabulus which they wrested from IS on Wednesday without significant resistance.

Anadolu agency said the rebels were destroying mines planted by IS.