Turkish war planes have launched air strikes on Kurdish positions in northern Syria, in a move likely to cause tensions with the US.
Turkey wants to oust these Kurdish fighters from Syria’s Afrin region, which lies near its southern border.
It considers them a terrorist group. But some were US allies in the battle against the Islamic State group.
Turkey had been shelling the area for two days, ahead of its declaration of a military operation on Saturday.
Russia – a key military figure in the region – says it is concerned by the development, and has relocated some of its troops based in the region. Officials earlier said Moscow would not interfere in the conflict.
Syria has previously warned against any operation and said it would shoot down Turkish planes.
Turkish Foreign Minister Mevlut Cavusoglu says Turkey has notified all actors involved – including the Syrian government – about the offensive.
What is happening in Afrin?
On Saturday, the Turkish army announced that a new air and ground campaign, dubbed “Olive Branch”, had launched at 14:00 GMT, targeting the Kurdish YPG (Syrian Kurdish People’s Protection Units) and Islamic State (IS) group jihadists.
The operation would be carried out “with respect for Syria’s territorial integrity”, it added. A later statement, reported by Reuters, said 108 targets belonging to Kurdish militants had been hit.
Pro-Turkey rebels, known as the Free Syrian Army, also began moving into the area, according to the state-run Anadolu news agency.
A spokesperson for the YPG told Reuters a number of people had been injured in the strikes on Afrin city and villages around it, but it is not yet clear how many.
Turkey’s military has been shelling the area since Thursday, a move which it said was in response to fire coming from the area.
On Saturday, the Syrian Democratic Forces (SDF) – an alliance against IS of which the YPG is a member – accused Turkey of using the bombardment as a smokescreen ahead of launching an offensive. A spokesperson for the group told Reuters news agency that it would have no choice but to defend itself if attacked.
Rizan Habou, of the Syrian Democratic Council in Afrin, told BBC Arabic that residents were seeking shelter.
“The YPG and the civilians will defend Afrin to the last moment,” he said.
Risks of opening new front ‘huge’
Mark Lowen, BBC Turkey correspondent, near border with Syria
In mid-afternoon the Turkish air strikes began, with plumes of smoke rising above Afrin. On the ground, Syrian rebel fighters backed by Turkey moved in, the military incursion rather inappropriately named Operation Olive Branch.
President Erdogan has vowed to wipe out a corridor, first Afrin and then the nearby town of Manbij, from where the YPG has failed to withdraw. Nobody can object when what we do is necessary, he said. We will get rid of these messy terrorists trying to invade our country.
But the risks are huge – the offensive pits Turkey against its Nato ally the US, which backs the Kurdish militia against IS, infuriating Ankara. Russia, which has troops in the area, has urged restraint – an MP in Moscow says it will be discussed at the UN.
The Syrian regime warned it would be seen as a violation of Syria’s sovereignty. An estimated half a million people have been killed in the Syrian war. With this new front, the danger is that number will rise again.
Why is Turkey’s targeting US-backed groups?
The YPG has been a key part of the battle against IS in Syria, and has been backed by the US.
Turkey, however, believes the group has links to the banned Kurdistan Workers Party (PKK), and has for several months been threatening to clear Kurdish fighters from Afrin and another city, Manbij, which lies 100km away.
Turkey’s military plans seem to have been accelerated by an announcement from the US that it will help the SDF alliance build a new “border security force” to prevent the return of IS.
The YPG and SDF deny any terrorist links – a claim backed by the US government.
But President Recep Tayyip Erdogan called the border force a “terror army”.
Disagreement over the Kurdish fighters has created a sharp division between the Nato allies.
The US state department has appealed for calm, and attempted to downplay portrayals of a new “border force”, instead characterising the new development as security training.
How are Russia and the US reacting?
Russia’s foreign ministry says it is concerned by news of the offensive, and is urging restraint.
Russian senator Frants Klintsevich – who is the deputy chairman of the defence and security committee – earlier told Interfax news agency that Moscow will only respond if Russian bases in Syria are threatened.
He said that Russia has been placed in a difficult situation, as it has “good relations with both Damascus and Ankara”.
Turkey’s military and intelligence chiefs had been trying to get Russia’s agreement to allow Turkish planes to use the Russian-controlled airspace above Afrin.
Such consent is seen as essential for any Turkish operation. Moscow is a key ally of Syrian President Bashar al-Assad and has a contingent of soldiers at the airport in the centre of Afrin.
It is not yet clear if Russia’s claim that it will not interfere precludes allowing use of its airspace.
Turkish Foreign Minister Mevlut Cavusoglu has reportedly discussed the military offensive with US Secretary of State Rex Tillerson, as did Turkey’s chief of military staff with his US and Russian counterparts.
However, no details of the conversations have been provided.