Turkey intensified its air and artillery strikes on Kurdish militia in northeast Syria on Friday, escalating an offensive that has drawn warnings of humanitarian catastrophe and turned Republican lawmakers against US President Donald Trump.
The incursion, launched after Trump withdrew US troops who had been fighting alongside Kurdish forces against ISIS terrorists, has opened a new front in the eight-year-old Syrian civil war and drawn fierce international criticism.
A war monitor gave a death toll approaching 100 from the first days of the assault, including 17 civilians as well as dozens of Kurdish fighters and Turkish-backed Syrian rebels. Turkey says nine civilians have been killed on its side of the frontier by retaliatory shelling.
In Washington, Trump - fending off accusations that he abandoned the Kurds, loyal allies of the United States - suggested Washington could mediate in the conflict. He also raised the possibility of imposing sanctions on Turkey, a move demanded by Republican congressional critics of his policy.
Trump's defence secretary, Mark Esper, told his Turkish counterpart that the incursion "risks serious consequences for Turkey" and Turkey must help find a way to "de-escalate the situation before it becomes irreparable", the Pentagon said.
On Friday, Turkish warplanes and artillery struck around Syria's Ras al Ain, one of two border towns that have been the focus of the offensive. Reuters journalists heard gunfire there from across the frontier in the Turkish town of Ceylanpinar.
Hundreds of kilometres further east along the frontier, Kurdish-led fighters reported heavy shelling in Qamishli, the biggest city in the Kurdish-controlled region of northeastern Syria. Authorities there said a car bomb had blown up in the city, killing three civilians and wounding nine. Video showed smoke rising from the wreckage.
A convoy of 20 armoured vehicles carrying Turkish-allied Syrian rebels entered Syria from Ceylanpinar. Some made victory signs, shouting "Allahu akbar" (God is greatest) and waving Syrian rebel flags as they advanced towards Ras al Ain.
Some 120 km (75 miles) to the west, Turkish howitzers resumed shelling near the Syrian town of Tel Abyad, a witness said.
"In these moments, Tel Abyad is seeing the most intense battles in three days," Marvan Qamishlo, a spokesman for the Kurdish-led Syrian Democratic Forces (SDF) said.
Overnight, clashes erupted at different points along the entire stretch of border from Ain Diwar at the Iraqi frontier to Kobani, more than 400 km to the west.
"The whole border was on fire," Qamishlo said.
Turkish forces have seized nine villages near Ras al Ain and Tel Abyad, said Rami Abdulrahman, director of the Syrian Observatory for Human Rights, which monitors the war.
At least 41 fighters with the SDF, 34 Turkey-backed Syrian rebels and 17 civilians have been killed in Syria, according to the Observatory. The SDF said 22 of its fighters were killed on Wednesday and Thursday.
Turkey says it has killed hundreds of SDF fighters and two Turkish soldiers have been killed. Turkish authorities said two people were killed and three wounded by mortar shelling in the border town of Suruc, raising the death toll to nine civilians killed on the Turkish side.
Turkey says the purpose of its assault is to defeat the Kurdish YPG militia, which it sees as an enemy for its links to insurgents in Turkey. It says it aims to set up a "safe zone" inside Syria, where it can resettle many of the 3.6 million refugees it has been hosting.
Turkey's President Tayyip Erdogan criticised Europe for failing to support the Turkish offensive and threatened to send refugees to Europe if the EU did not back him. That prompted a furious response from the EU.
"We will never accept that refugees are weaponised and used to blackmail us," European Council President Donald Tusk tweeted. France said sanctions against Turkey would be discussed at an EU summit next week.
The International Rescue Committee aid group says 64,000 people in Syria have fled in the first days of the campaign.
The Kurdish YPG is the main fighting element of the SDF, which has acted as the principal allies of the United States in a campaign that recaptured territory from ISIS.
The SDF now holds most of the territory that once made up Islamic State's "caliphate" in Syria, and has been keeping thousands of fighters from the terrorists group in jail and tens of thousands of their family members in camps.
A camp sheltering more than 7,000 displaced people in northern Syria is to be evacuated and there are talks on moving a second camp for 13,000 people, including militants' families, after both were shelled, Kurdish-led authorities said.
Two Turkish officials said Ankara believed there were more than 1,000 ISIS fighters, mostly foreigners, held in the part of Syria where Turkey aims to set up its safe zone. Turkey would aim to send them to their countries of origin.
Medecins Sans Frontieres said a hospital in Tel Abyad had been forced to shut after most of its staff fled.
Rare Republican Criticism Of Trump
In the United States, Trump's decision to withhold protection from the Kurds mhas been one of the few issues to prompt criticism from his fellow Republicans, including leading allies on Capitol Hill such as Senator Lindsey Graham.
Trump said in a Twitter post on Thursday: "We have one of three choices: Send in thousands of troops and win Militarily, hit Turkey very hard Financially and with Sanctions, or mediate a deal between Turkey and the Kurds!".
"I hope we can mediate," Trump said when asked about the options by reporters at the White House.
Without elaborating, he said the United States was "going to possibly do something very, very tough with respect to sanctions and other financial things" against Turkey.
Western countries' rejection of the Turkish offensive creates a rift within the NATO alliance, in which Turkey is the main Muslim member. NATO Secretary General Jens Stoltenberg said after talks with Foreign Minister Mevlut Cavusoglu in Istanbul that he expected Turkey to act with restraint. Cavusoglu said Ankara expected "strong solidarity" from the alliance.