US Defense Secretary Jim Mattis says Washington and Ankara have had high-level communication about the operation and Turkey had informed the US before Operation Olive Branch started.
Turkey gave Washington advance warning before launching an operation against YPG/PKK in Afrin, and Ankara has "legitimate" security concerns in the area, Defense Secretary Jim Mattis said on Sunday.
"Turkey was candid. They warned us before they launched the aircraft they were going to do it in consultation with us, and we are working now on the way ahead through the ministry of foreign affairs," Mattis told reporters aboard his aircraft at the start of a trip to Asia.
Turkey "is the only NATO country with an active insurgency inside its borders, and Turkey has legitimate security concerns," Mattis said, referring to the PKK terrorist organisation, which has been engaged in a separatist struggle against Ankara since 1984.
Mattis said Turkish and American parts have had high-level communication about the operation including military officials.
"We are very alert to it. Our top levels are engaged … and we're working through it," Mattis said. "We'll work this out."
Turkey launched Operation Olive Branch, an offensive by Ankara's troops and allied Free Syrian Army (FSA) against the YPG in the town of Afrin.
TRT World's Courtney Kealy reports.
The US military currently has about 2,000 personnel in Syria but no US forces are at risk because of the Turkish offensive "at this time," Mattis said.
The YPG has been a key US ally in the war against Daesh, helping to drive the group's militants from swathes of Syrian territory, including its stronghold Raqqa.
PYD and its armed wing the YPG, which is the Syrian offshoot of the PKK, all look to Abdullah Ocalan as their guide.
Ocalan and his PKK group are recognised as terrorists by the US, EU and Turkey.
Since the mid-1980s, the PKK has waged a wide-ranging terror campaign against the Turkish state in which an estimated 40,000 people have been killed.
More than 1,200 security personnel have been martyred since July 2015 when the group resumed its terror campaign against the Turkish state following a fragile almost two-and-a-half year ceasefire.
UN to discuss Syria, Afrin operation
The UN Security Council will on Monday discuss the humanitarian crisis in Syria and the Turkish offensive against the YPG in Afrin, diplomats said.
The council was already scheduled to meet to hear a report from UN aid chief Mark Lowcock on his recent visit to Syria.
At France's request, the closed-door consultations will also touch on the Syrian campaign in Idlib and Eastern Ghouta, as well as the latest Turkish operation, diplomats said on Sunday.
Russia, which supports the Syrian regime, also voiced concern. The defence ministry said it was withdrawing its troops from Afrin to prevent any "provocation."
Meanwhile, Turkish Foreign Minister Mevlut Cavusoglu warned the United Nations against condemning Ankara's anti-YPG operation in Afrin, saying the move would have repercussions.
In the third day of the operation, nine villages in the north of Afrin were cleared of YPG/PKK by the Turkish army and the FSA.
Turkish Chief of General Staff Hulusi Akar said that the Turkish Armed Forces are taking all precautions to prevent civilian deaths.
The Turkish Armed Forces (TAF) on Sunday announced that it had destroyed 45 targets that were identified as shelters, ammunition depots used by the YPG during Operation Olive Branch. The 32 fighter jets that participated in the operation returned to their bases to prepare for the next one.