Turkish presidential spokesman Ibrahim Kalin said the goal was to drive Islamic State from a 90-km strip of land along the border with Turkey, which has been buffeted by a spate of bombings, blamed on the group, that have killed scores.
"Starting from Jarablus, the cleansing of this region is our priority," Kalin told a news briefing. "We have already cleansed 400 square km successfully."
Turkey has long said it wants a "buffer zone" in the area, although it has not used the term during this incursion.
As well as driving out the ultra-hardline Islamists, it also wants to prevent Kurdish forces taking territory that will let them join up cantons they control in northeast and northwest Syria.
Turkey frets that seizing such a broad swathe of territory could embolden Kurdish PKK insurgents on Turkish soil.
