Turkey advised the United States ahead of its air strikes in Syria against US-backed Kurdish militia, and Washington is in contact with Ankara about the way forward, US Defense Secretary Jim Mattis said on Sunday during a flight to Asia.

"Turkey was candid," Mattis said, without disclosing the US reaction to Turkey's notification. "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. We'll work this out."
Turkey's air strikes in Syria's Afrin province open a new front in the country's nearly 7-year-old war.
The operation pits Turkey against Kurdish fighters allied with the United States at a time when ties between Ankara and Washington - North Atlantic Treaty Organization allies and members of the coalition against Islamic State - appear dangerously close to a breaking point.
Turkey has long been outraged at US backing of YPG militia in Syria, which Ankara views an extension of the outlawed Kurdistan Workers Party (PKK). The PKK has carried out a deadly, three-decade insurgency in Turkey's mainly Kurdish southeast.
"Turkey has legitimate security concerns," Mattis said, noting it was the only NATO ally with an active insurgency inside its borders.
At the same time, Mattis said the US military was deployed in Syria in a way that allowed it to ensure that US-provided weaponry was being used to battle insurgents, not Turkey. That support has allowed the US-led coalition to crush Islamic State, he said.
"They (the Kurdish and other US-backed fighters) have proven their effectiveness," Mattis said. "It has cost them thousands of casualties. But you have watched them, with the coalition support, shred (the) ISIS caliphate in Syria."
So far, that argument has failed to soothe Ankara's concerns, however.
Mattis said Turkey's military informed Washington of its air operation in a phone call to high levels of the US military. He said no US forces were currently at risk from the Turkish operations.
Asked whether he was concerned about the situation, Mattis said: "We are very alert to it. Our top levels are engaged ... And we're working through it."