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 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 United States-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.

On Wednesday, 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.