Turkish ground forces advanced into northern Syria's Afrin region on Sunday, Ankara said after launching artillery and air strikes on a US-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 organisation by Turkey, said it had repulsed the Turkish forces and their allies after fierce clashes.
Intense Turkish artillery fire and air strikes continued to hit some villages, the YPG said, and fierce battles raged to the north and west of Afrin against Turkish forces and their Syrian rebel allies, said Birusk Hasaka, the YPG spokesman in Afrin.
Turkey opened a new front in the nearly seven-year-old Syrian war on Saturday when, under what Ankara has called "Operation Olive Branch", Turkish artillery and air strikes pounded YPG positions in Afrin.
Turkey is targeting the US-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 US is backing the YPG in Syria, seeing it as an effective partner in the fight against Islamic State.
Prime Minister Binali Yildirim said the Turkish military, NATO's second-largest, would create a 30-km (19-mile) "safe zone" in the region, according to broadcaster HaberTurk.
"Our jets took off and started bombing. And now the ground operation is underway. Now we see how the YPG ... are fleeing in Afrin," President Tayyip Erdogan said. "We will chase them. God willing, we will complete this operation very quickly."
Around 25,000 Free Syrian Army rebels are taking part in the operation with the goal of recapturing Arab towns and villages seized by the YPG almost two years ago, a rebel commander said.
Major Yasser Abdul Rahim said the rebels did not seek to enter the mainly Kurdish city of Afrin but encircle it and expel the YPG, which controls it.
A main goal of the military operation was to recapture Tel Rifaat, a town southeast of Afrin, and a string of Arab villages the YPG captured from rebels in February 2016, driving out tens of thousands of inhabitants, Abdul Rahim told Reuters.
Rocket hits Turkish town
A rocket fired across the border from Syria hit the Turkish border town of Reyhanli on Sunday, killing a Syrian national and wounding 32 people, broadcaster NTV reported the town's mayor as saying. CNN Turk said three rockets in total had been fired across the border towards Reyhanli.
Erdogan said some of Turkey's allies had provided the YPG with 2,000 plane shipments and 5,000 truckloads of ammunition, comments that appeared to be aimed at the US.
The attacks follow weeks of warnings against the YPG in Syria from Erdogan and his ministers. Turkey has been particularly outraged by an announcement that the US planned to train 30,000 personnel in parts of northeast Syria under the control of the YPG-led Syrian Democratic Forces.
Foreign Minister Mevlut Cavusoglu told reporters anyone who opposed the action in Afrin was siding with terrorists and would be treated accordingly.
He said Ankara expected France to support Turkey's operation, after France asked Ankara to act with restraint and said it would call an emergency meeting of the UN Security Council.
Turkey-backed Free Syrian Army rebel factions had captured a Kurdish village with no resistance and were clearing landmines, a Turkish official said.
The YPG said it had repulsed the Turkish forces.
"All the Turkish military's ground attacks against Afrin have been repelled so far and they have been forced to retreat," Nouri Mahmoudi, a YPG official, said. Since the morning, the combatants have exchanged shelling and clashed along several frontlines around Afrin, he said.
Thousands rallied against the attacks in the border town of Amuda in northwest Syria, vowing to stand against "Turkish occupation", according to a local witness.
The Turkish military said it had hit targets including hideouts used by Kurdish militants. The YPG said Turkey's strikes killed some civilians and accused Turkey of striking civilian districts and a camp for displaced people in Afrin.
Western governments have largely urged calm, with the US saying the focus should be on fighting Islamic State in Syria.
Russia, which backs Syrian President Bashar al-Assad in the civil war, will demand in the UN that Turkey halt it's operation in Afrin, RIA news quoted a member of the Russian parliament's security committee as saying on Saturday.
At a training camp near the border, about 200 fighters from the Turkey-backed Free Syrian Army factions drilled on a parade ground, some in different khaki-coloured uniforms, some in jeans.
Lieutenant-colonel Mohammad al Hamadeen, a rebel spokesman, said a ground offensive was due to begin within hours against the YPG.
"The military operation started this morning with the invasion of the north-western areas of Afrin. And they will start in the eastern area of Afrin," he told Reuters.
A Reuters reporter on the outskirts of the northern Syrian town of Azaz, under the control of Free Syrian Army factions, heard several blasts and saw smoke rising from a hill to the west, where a fighter said the YPG were.
There were no signs of conflict in the town itself, where life appeared to continue as normal with traffic on the muddy, potholed roads and uniformed rebel police at the main roundabouts. At a car repair workshop on the outskirts of the town some men were fixing a gun-loaded vehicle.
On Saturday, a Pentagon official said: "We encourage all parties to avoid escalation and to focus on the most important task of defeating ISIS (Islamic State)."
Turkey's state-run Anadolu news agency reported that four rockets fired from Syria hit the border town of Kilis overnight, damaging houses. Turkish security forces retaliated, it said.