The operation is being carried out under the framework of Turkey's rights based on global law, UN Security Council resolutions, its self-defense rights under the UN charter, and respect for Syria's territorial integrity, it said.
US Secretary of State Rex Tillerson said Monday he was "concerned" about the offensive, while European Union diplomatic chief Federica Mogherini said she would discuss the situation with Turkish officials.
Syrian Turkmen militia are participating in this operation on the side of the Turkish army. "It was a threat made against us", Levent told AP through Husseyin, who acted as an interpreter.
Russian Federation - another key player in the multi-sided Syrian Civil War and the main backer of Syria's dictatorial President Bashar al-Assad - has thus far failed to react beyond a limited statement that expressed Moscow's concern for the uptick in violence.
The operation puts Turkey at odds with the U.S., which has logistically supported the Kurdish fighters as part of the fight against Islamic State.
Plans for the operation are believed to have accelerated when U.S. officials said earlier this month that it would help the Syrian Democratic Forces (SDF) alliance, which is dominated by the YPG, build a new "border security force" to prevent the return of IS.
Opening a almost weeklong trip to Europe on Monday amid a government shutdown back home, Tillerson went to the embassy to greet the USA ambassador to Britain. It is not clear how many Turkish soldiers are on the ground.
But Turkey said Washington must end its support for the Kurdish YPG militia before any proposal for cooperation. We know that many countries, including the United States, say that the fight against Daesh would be impossible without the help of YPG militants, but it is rather a pretext to hide other intentions.
After the Turkish General Staff has announced the launch of the operation dubbed the "Olive Branch" in Afrin against the PKK and the YPG on Saturday, the SDF expressed readiness to "defend ourselves and our people".
Earlier a spokesman for the Kurdish forces that control the Afrin area also reported the raids.
In a report by AFP, the air raids killed civilians including eight members of the same family who had fled fighting elsewhere, a war monitor said. "There is also Manbij and east of the Euphrates River", Foreign Minister Mevlut Cavusoglu said in Vancouver, Canada last week.
Dictator Bashar al-Assad, technically the head of government for the territory being invaded, has also decried the "brutal Turkish aggression" against the Kurds.
Western powers, including the United Kingdom and France, have urged restraint in order to avoid civilian casualties.
But Erdogan expressed impatience with U.S. demands to set a clear timetable, saying the campaign would be over "when the target is achieved".
The United Nations has said it is deeply concerned for the more than 300,000 people in Afrin.