Syrian rebels supported by Turkish and coalition air strikes pushed further west into areas held by Islamic State in northern Syria as Ankara and its allies step up a campaign to rout the jihadists from the border area.

Turkish strikes destroyed three buildings used by IS around the villages of Kunduriyah and Arab Izzah, about 30 kilometres (18 miles) west of the border town of Jarabulus, the army said in a statement.

The pro-Ankara rebels took Jarabulus from IS last week on the first day of an unprecedented Turkish offensive aimed both at IS and a US-backed Kurdish militia that had been leading the fight against the jihadists.

In the last few days the rebels have been moving quickly to clear the jihadists from the last stretch of the border under their control, backed by Turkish artillery and Turkish and coalition air strikes.

The army said the area around Kunduriyah was now controlled by the opposition rebels.

An AFP photographer at the border said Turkish-led forces were undertaking operations near the town of Al-Rai, about 20 kilometres further west.

On Thursday, Pentagon spokesman Captain Jeff Davis estimated IS only retained control of about 25 kilometers of the border, east of Al-Rai.

Turkey sent tanks and troops into Syria on August 24 to both combat IS -- which has been blamed for a string of suicide attacks inside Turkey -- and halt the westward advance of the Kurdish People's Protection Militia (YPG).

Turkey sees the YPG as a terror offshoot of the Kurdistan Workers Party (PKK) waging a bloody three-decade insurgency on its soil.

The Turkey-Kurdish fight is yet another complication in Syria's tangled civil war, with both Turkey and the US seeking to retake territory from IS jihadists by supporting different proxy groups.

Washington, which backs the YPG, on Monday expressed alarm at Turkey's bombardments of the group and called on its two allies to remain focused on fighting IS.

- Kurdish protesters teargassed -

Ankara has said the YPG will remain a target unless it returns east of the Euphrates river into the two cantons under Kurdish control.

On Friday, Turkish President Recep Tayyip Erdogan dismissed US claims that the YPG-led Syrian Democratic Forces (SDF) had retreated to the northeast, as demanded.

"Right now, people say they have gone to the east but we say no, they haven't crossed," Erdogan said.

A US defence official in Washington, who requested anonymity, said that any continuing presence by the YPG in the area was "completely insignificant".

Turkey's operation against the YPG has raised tensions with Syrian Kurds in other areas.

On Friday, Turkish security forces fired tear gas and water cannon at stone-throwing protesters in the Syrian border town of Kobane, which Kurdish militia took from IS in 2015 after a lengthy battle.

The demonstrators were protesting the route of a five-kilometre wall being built by the Turks between Kobane and the Turkish town of Suruc.