The air and ground offensive -- the most ambitious launched by Ankara in the Syria conflict -- made rapid progress towards Jarabulus with rebel fighters already proclaiming victory by the late afternoon just 14 hours after it started.
"Jarabulus is completely liberated," Ahmad Othman, commander of the Sultan Mourad rebel group, told AFP from the scene, while another rebel spokesman said IS fighters had fled towards Al-Bab to the southwest.
But visiting US Vice President Joe Biden reassured Turkey that Washington had told the Kurdish fighters under no circumstances to cross west of the Euphrates River or face the total loss of American support.
The operation -- named "Euphrates Shield" -- began at around 4:00 AM (0100 GMT) with Turkish artillery pounding dozens of IS targets around Jarabulus.
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Turkish F-16 fighter jets, backed by US-led coalition war planes, also hit targets inside Syria.
As well as tanks, an AFP photographer in the area of Karkamis opposite Jarabulus saw several smaller military vehicles believed to be carrying the pro-Ankara Syrian rebels.
Security sources quoted by Turkish television said a small contingent of special forces had travelled into Syria to secure the area before the larger ground operation.
Turkey wants to show it is serious about taking on IS, which has been blamed for a string of attacks inside the country -- the latest a weekend attack on a Kurdish wedding in Gaziantep that left 54 people dead, many of them children.
Ankara was long accused of turning a blind eye to the rise of IS in Syria and even aiding its movements to-and-fro across the border, claims the government had always vehemently denied.
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