Turkey has launched an offensive into north-eastern Syria, unleashing air strikes and artillery barrages aimed at US-backed Kurdish forces who control the region.
Video footage showed civilians fleeing towns with columns of smoke rising in the background and jet trails visible in the sky. Activists and observers say at least seven civilians have been killed so far.
Turkey???s offensive was triggered by a call between Donald Trump and Turkey???s president, Recep Tayyip Erdo??an, on Sunday, in which the Turks claim Trump handed over leadership of the campaign against Isis in Syria to Ankara. The American president announced on Sunday night that US troops would withdraw from the region.
On Wednesday, hours after the bombing had begun, Trump issued a statement mildly criticising the offensive aimed at Kurdish forces which for nearly five years fought alongside the US against Isis.
???This morning, Turkey, a Nato member, invaded Syria. The United States does not endorse this attack and has made it clear to Turkey that this operation is a bad idea,??? the statement said, before noting: ???There are no American soldiers in the area.???
The UN security council is due to convene on Thursday to discuss the offensive at the request of its five current European members, but it is not expected to deliver a strong rebuke to Turkey, given tacit Russian support and US ambivalence. France was pushing for the council to at least make a joint statement but it was unclear on Wednesday whether even that would be possible.
The Nato secretary general, Jens Stoltenberg, called on Turkey to act with restraint and ???ensure that the gains we have made in the fight against Isis are not jeopardised. I will discuss this issue with President Erdo??an Friday.???
The Turkish leader marked the launch of the offensive, dubbed Operation Peace Spring, with a tweet, saying that it was being conducted by Turkish and Turkish-backed Syrian militias, against Kurdish forces and Isis.
???Our mission is to prevent the creation of a terror corridor across our southern border, and to bring peace to the area,??? the president wrote.
Turkey says it is seeking to establish a 20-mile (32km) deep buffer zone along the border to secure the country against the threat of what it says are Kurdish terror groups as well as Isis. It also hopes to resettle Syrian refugees in the zone.
Mustafa Bali, spokesman for the Kurdish-led Syrian Democratic Forces (SDF) ??? which Ankara considers an extension of the outlawed Kurdistan Workers??? party (PKK) ??? confirmed shortly after Erdo??an???s announcement that Turkish warplanes had already begun attacking the region, creating a ???huge panic among people???. An SDF soldier shared photographs of plumes of smoke, which he said was the result of airstrikes and artillery fire near the border town of Ras al-Ayn.
The Syrian Observatory for Human Rights, a UK-based war monitor, said civilians in Ras al-Ayn and neighbouring villages had begun fleeing deeper inside the Kurdish-held region. Qamishli and Ain Issa, key administrative centres for the SDF, were hit by airstrikes, a spokesman said.
In his statement on Thursday, Trump said: ???Turkey has committed to protecting civilians, protecting religious minorities, including Christians, and ensuring no humanitarian crisis takes place ??? and we will hold them to this commitment.
???In addition, Turkey is now responsible for ensuring all Isis fighters being held captive remain in prison and that Isis does not reconstitute in any way, shape, or form,.???
It is far from clear how Turkey would take custody, let alone responsibility for the 90,000 men, women and children with links to the terror group currently held by the Kurds.
The largest camp for women and children, al-Hawl, is home to 74,000 people, and lies outside the parameters of the proposed safe zone.
Hassan Hassan, an expert on Isis at the Centre for Global Policy, said the terror group was bound to benefit from Turkey???s incursion.
???The SDF had fresh and raw intelligence on people who joined Isis and the structures of Isis. Now Turkey comes in and doesn???t have access to much of this information,??? Hassan, co-author of Isis: Inside the Army of Terror, said. He added: ???The areas in Syria currently controlled by Turkey are full of corruption, more corrupt even than regime areas. Isis would have no trouble buying loyalty, paying bribes to escape. So definitely Isis will have new opportunities.???
Isis claimed an overnight suicide attack by two of its fighters in its former capital of Raqqa, which killed and injured 25 people.
The SDF, a US-backed force, is Turkey???s main target.
Meanwhile, forces belonging to the Syrian president, Bashar al-Assad, have also been on the move to the south of Syria???s Kurdish-held region, leaving the SDF pinched between the two.
While Trump has sent mixed signals over the Turkish invasion, and the state department remained silent, politicians from both US parties vowed to inflict severe sanctions on Turkey.
???Turkey must pay a heavy price for attacking our Syrian Kurdish partners,??? Democratic senator Chris van Hollen said on Twitter. ???Senators on both sides of the aisle won???t support abandoning the one regional group most responsible for putting Isis on its heels. Our bipartisan sanctions bill is being finalised now.???
The earliest sanctions legislation can be proposed is next week when Congress returns from recess.
???I have serious concerns about the unilateral military action that Turkey has taken,??? the UK???s foreign secretary, Dominic Raab, said. ???This risks destabilising the region, exacerbating humanitarian suffering, and undermining the progress made against Daesh [Isis] which should be our collective focus.
???Turkey has shown considerable generosity in hosting so many Syrian refugees. But we will not support plans for returns until the conditions are in place for a voluntary and safe return home.???
Aid groups have warned of a humanitarian catastrophe as thousands flee the expected fighting and re-emergence of Isis. The SDF says it has already withdrawn some soldiers from the prisons and camps holding Isis members to focus on the defence against Turkey, raising fears that Isis sleeper cells could liberate those inside.
Save the Children which works with more than 100,000 refugees from Isis living in the region, warned that the 9,000 children there were particularly vulnerable.
Sonia Khush, the Syria response director with the charity, warned that ???any interruption to camp services which are already overstretched would put lives at risk???.
Kurdish leaders in the area issued a general mobilisation call, urging civilians to ???head to the border with Turkey ... to resist during this delicate historical moment???. The SDF has resumed digging trenches and tunnels in the border areas, covering streets with metal canopies and stockpiling tyres to burn to block Turkish drone cameras.
Kurdish officials also said that they have asked Russia, Assad???s major ally, to facilitate a dialogue with Damascus. The Kurds risk losing the autonomy they won during Syria???s eight-year-old war by realigning with the Syrian regime but such a move is likely to stave off the worst of a Turkish attack.
A secondary goal of Turkey???s Operation Peace Spring is to repatriate up to 2 million of the country???s 3.6 million Syrian refugees inside the planned border zone. The Kurds say Ankara???s real goal is to dilute their demographic dominance of the north-east with an influx of mostly Sunni Arab refugees originally from other parts of Syria.