Turkey has shelled more targets in north-west Syria and says it will swiftly crush US-backed Kurdish YPG fighters in an air and ground offensive on the Afrin region beyond its border.
- US, Germany express concern over operation
- Kurdish forces say 18 were civilians killed
- Turkey urges Washington to end support for YPG militia
Kurdish fighters said at least 18 civilians, including women and children, had been killed in the offensive by Turkish troops and allied Syrian rebels.
The three-day-old campaign has opened a new front in Syria's multi-sided civil war, realigning a battlefield where outside powers are supporting local combatants.
While Washington and other Western capitals expressed concern, Turkish President Tayyip Erdogan said he had secured a go-ahead for the campaign from Russia, principal backer of Syrian President Bashar al-Assad, long Turkey's foe.
Turkish forces and their Syrian anti-Assad rebel allies began their push on Saturday to clear the north-western border enclave of Kurdish YPG fighters.
Ankara considers the YPG to be allies of insurgents that have fought against the Turkish state for decades.
The United States, meanwhile, has armed and aided the YPG as its main ground allies against Islamic State militants.
France called for an emergency meeting of the United Nations Security Council on Monday, and Britain said it would look for ways to prevent any further escalation.
But Mr Erdogan said Turkey was determined to press ahead.
"There's no stepping back from Afrin," he said in a speech in Ankara.
"We discussed this with our Russian friends, we have an agreement with them, and we also discussed it with other coalition forces and the United States."
White House issues warning to Turkey
The White House warned that the campaign risked exacerbating a humanitarian crisis and disrupting what had been a stable area.
"We urge Turkey to exercise restraint in its military actions and rhetoric, ensure that its operations are limited in scope and duration, ensure humanitarian aid continues and avoid civilian casualties," White House spokeswoman Sarah Sanders told a briefing.
German Foreign Minister Sigmar Gabriel also expressed concern, calling his Turkish counterpart to express concerns about the possible effect on civilians.
US Secretary of State Rex Tillerson said Washington had proposed working with Turkey and forces on the ground in Afrin to "see how we can stabilise this situation and meet Turkey's legitimate concerns for their security".
But Turkey said Washington must end its support for the Kurdish YPG militia before any proposal for cooperation.
"If they want a cooperation, we are ready for this cooperation," Deputy Prime Minister Bekir Bozdag told reporters after a cabinet meeting.
"As the first step to take, they can stop arming terror groups and take back weapons already given."
Syria has objected to the Turkish incursion, and Moscow, which controls parts of Syrian air space on behalf of its allies in Damascus, has not confirmed giving a green light to it.
But Russia does not appear to be acting to prevent it, and has pulled its own troops out of the Afrin area.
Iran, Mr Assad's other main military supporter, called for a halt to the operation.
Foreign Ministry spokesman Bahram Qassemi said the Afrin campaign could lead to "the return of regional terrorism and extremism", according to state television.
The YPG's Afrin spokesman, Birusk Hasaka, said there were clashes between Kurdish and Turkish-backed forces on the third day of the operation, and that Turkish shelling had hit civilian areas in Afrin's north-east.
Afrin would be a "quagmire from which the Turkish army will only exit after suffering great losses", said a statement from the YPG-led Syrian Democratic Forces umbrella group.
The YPG said Afrin had already been reinforced in anticipation of the Turkish offensive, and there were discussions over whether to send more reinforcements from other YPG-held territory, which is separated from Afrin by areas held by Syrian government forces.
The United Nations has said it is deeply concerned for the more than 300,000 people in Afrin.