Turkish ground forces pushed into northern Syria's Afrin province on Sunday, the army said, after Turkey launched artillery and air strikes on a U.S.-backed Kurdish militia it aims to sweep from its border.
The Syrian-Kurdish YPG militia, supported by the United States but seen as a terrorist organization by Turkey, said it had repulsed the Turkish forces and their allies after fierce clashes.
It marked the second day of fighting after Ankara opened a new front in the nearly seven-year-old Syrian war. Under what the Turkish government has called "Operation Olive Branch", Turkish air strikes on Saturday pounded YPG positions in Afrin.
Turkey is targeting the U.S.-backed fighters at a time when ties with ally Washington appear close to breaking point.
Turkey sees the YPG as an extension of the outlawed Kurdistan Workers Party (PKK) which has carried out a deadly, three-decade insurgency in Turkey's mainly Kurdish southeast. The United States is backing the YPG in Syria, seeing it as an effective partner in the fight against Islamic State.
"The Olive Branch Operation is going on as planned, and the ground operation has started," the Turkish army, NATO's second-largest, said. Prime Minister Binali Yildirim said the operation would create a 30-km (19-mile) "safe zone", according to broadcaster HaberTurk.