Recent statements by US military officials about plans to train border security forces that would protect a Kurdish enclave in Syria also provoked Turkey's ire.
"We are taking these steps to ensure our own national security," President Recep Tayyip Erdogan said in comments carried by the semiofficial Anadolu agency.
Yet Turkish incursions could carry risks. The Government of Syrian President Bashar al-Assad had warned that it was prepared to fire on Turkish warplanes in the event of an attack on Afrin.
A Syrian government offensive is causing one of the worst surges in population displacement since Syria's civil war began. More than 212,000 people have fled fighting around Idlib in the past month.
Yesterday, hours after the announcement of the airstrikes, Turkey said it had struck more than 100 positions belonging to Kurdish fighters. The number of casualties was not immediately clear. The airstrikes followed days of intense Turkish artillery fire on Kurdish positions, according to residents in Afrin.
In a statement, the US-backed Kurdish force, known as the Syrian Democratic Forces, warned that the Turkish offensive "threatens to breathe new life into Daesh (Isis)". . The Trump Administration, in urging Nato-ally Turkey not to attack, had made a similar argument, saying it would distract from the battles against Isis militants in their remaining strongholds in Syria.
Much about the Turkish offensive, which the Government dubbed "Operation Olive Branch," remained unclear.
Aaron Stein, of the Atlantic Council, said: "Afrin will be hostile to a Turkish-backed force patrolling from permanent garrisons. The YPG [Syrian Kurdish militia] in the area can retreat to the mountains for protection".
The offensive probably was prompted in part by Turkish concerns that Russia and the US planned to broker a reconciliation between Syria's Government and the Syrian Kurdish forces. "This is anathema to Turkey for obvious reasons," Stein said. "So they are making a statement."Washington Post