Turkey warned the United States before carrying out airstrikes against U.S.-backed Kurdish militia in Syria's Afrin province, Defense Secretary James Mattis said Sunday, according to a report by Reuters.
"Turkey was candid," the defense secretary said on a flight from Asia, the Reuters report said. "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 military told Washington of the air operation in a phone call to high level US military officials, Reuters reported. No US forces were at risk from the Turkish military operations, said Mattis, who did not disclose the US reaction to Turkey's warning, Reuters said.
On Sunday, Turkey launched a ground operation across the border into northern Syria, in a move likely to raise tensions with the United States.
Turkish officials said the troops entered the Afrin area a day after Turkish jets pounded targets there in an attempt to drive US-allied Kurdish militia from the area. "Operation Olive Branch is ongoing as planned and the ground operation has started," the Turkish armed forces said in a statement.
The land operation came hours after Turkish jets targeted US-backed, Syrian-Kurdish YPG militia in the area, killing at least eight people and injuring 13, according to the Syrian Democratic Forces General Command.
The military incursion is likely to raise tensions between Turkey and the United States, which supports and openly arms Kurdish militias fighting ISIS.
Turkish President Recep Tayyip Erdogan said the operation would be completed "in a very short time," during a public address Sunday in the city of Bursa, according to the Turkish state-run news agency Anadolu.
Rockets from Syria hit Turkish city
The land operation comes as YPG missiles fired from Syria hit the Turkish border town of Reyhanli on Sunday, according to Turkey's Deputy Prime Minister Bekir Bozdag. One Syrian national was killed and 32 wounded in the attack, the town's mayor said on Turkish broadcaster NTV.
Syrian President Bashar al-Assad denounced what he called "Turkish brutal aggression on the Syrian city of Afrin," according to the state-run Syrian Arab News Agency.
Earlier in the day, rockets fired from Syria also hit the Turkish border city of Kilis, according to Anadolu. One person was injured and buildings damaged in the attack, said local governor, Mehmet Tekinarslan.
It was not immediately clear who fired the rockets, though they followed Turkish airstrikes on areas under the control of the People's Protection Units, also known as the YPG.
Operation Olive branch
Turkey said it launched what it dubbed Operation Olive Branch on Saturday to target "terrorist organizations" including YPG forces.
The Turkish Air Force has destroyed 45 targets, including barracks, hideouts, weapon depots and gun positions in strikes on northern Syria's Afrin region, the armed forces said in a statement Sunday.
Turkey has long fought Kurdish unrest in the southeastern part of the country. It's determined to prevent the establishment of a Kurdish state across the border in Syria and has used military force in the past against Kurds and ISIS in the northern part of the neighboring country.
Turkey 'targeting terrorists,' YPG calls attacks 'barbaric'
Turkish Foreign Affairs Minister Mevlut Cavusoglu said in a tweet Saturday that the operation isn't targeting civilians and "innocent Syrians" -- just terrorists.
He told a news outlet that the Syrian government was informed of the operation in advance, but the Syrian government, speaking through the state-run news agency SANA, said it wasn't notified.
The YPG issued a statement on a pro-PKK news outlet, ANF, calling the Turkish attack "barbaric."
"We have no choice but to resist," the YPG statement said. "We call upon all of our young people to meet in the ranks of resistance, taking the resistance spirit of our sacrificial martyrs as an example."
France on Sunday requested an urgent meeting of the UN Security Council to discuss ongoing developments in the Syrian areas of Afrin, Idlib and Ghouta, the country's Foreign Minister Jean-Yves Le Drian said in a tweet on Sunday.
Le Drian called for ceasefires "everywhere" and unconditional humanitarian access. Rebel-held areas of Idlib and Ghouta in northern Syria have come under sustained attack by Syrian regime forces, raising fears for the thousands of civilians sheltering there.
Meanwhile German Foreign Minister Sigmar Gabriel said the "military confrontation" between Turkish and US-backed Kurdish forces in northern Syria "entails unpredictable risks," in a tweet on Sunday. "Everyone's efforts need to aim at making progress in the political process," he said.
The Iranian Foreign Ministry on Sunday also called for Turkey's operation in Afrin to be "completed immediately" and for the prevention of a crisis in the border region of Turkey and Syria, according to state-run news agency IRNA.
Washington urges restraint
Washington had previously called on Ankara to refrain from launching a military incursion in Syria. "The focus needs to be on ISIS," State Department spokeswoman Heather Nauert said last week.
Turkish forces have said they are targeting ISIS as well as Kurdish militia in Afrin.
"The operation is being carried out within the right of self-defense and with respect to Syrian territorial integrity," the Turkish armed forces said in a statement.
US-trained border force in Manbij
The incursion is likely to further stoke tensions between Turkey and the US after the announcement of a US-backed border force in Manbij, northern Syria, last week. A 30,000-strong, US-trained border force from the Syrian Democratic Forces, dominated by YPG fighters, is to be trained in Manbij. Turkish-backed rebels and US forces have been trading fire there, US defense officials said.
The SDF is made up of a number of local rebel groups but mainly from Kurdish militia of the YPG.
The announcement of a border force infuriated Turkey's leaders, and Erdogan has accused the United States, its most powerful NATO ally, of "building an army of terror" on his border and threatened to "drown" the US-backed force. Turkey regards the YPG as the Syrian arm of the Kurdistan Workers' Party, or PKK, despite the group's help in battling ISIS.