Turkey has pressed on with its assault in northern Syria for a second day, reportedly causing around 60,000 people to flee their homes and putting nearly half a million people at risk.
The region has been pounded with air strikes and an artillery bombardment that raised columns of black smoke along the border and sent panicked civilians scrambling to get out.
The UN refugee agency said tens of thousands were on the move, and aid agencies warned that nearly a half-million people near the border were at risk.
Syrian Observatory for Human Rights said that since Wednesday "more than 60,000 fled border areas", adding that most of those had travelled east towards Hasakeh.
Earlier, it emerged that a Turkish civil servant and a nine-month-old Syrian baby had been killed after mortars were fired from northern Syria into the Turkish border town of Akcakale.
The Turkish air and ground assault was launched three days after US President Donald Trump opened the way by pulling American troops from their positions near the border alongside their Kurdish allies.
That move drew swift criticism from Republicans and Democrats in Congress, along with many national defence experts, who say it has endangered not only the Kurds and regional stability but US credibility as well.
The Syrian Kurdish militia was the only US ally in the campaign that brought down the Islamic State group in Syria.
Mr Trump urged Turkey to be moderate in its approach and safeguard civilians.
But the opening barrage showed little sign of holding back: The Turkish Defence Military said its jets and artillery have struck 181 targets so far.
More than a dozen columns of thick smoke rose in and around the town of Tel Abyad, one of the offensive's first main targets.
Turkish officials said the Kurdish militia had fired dozens of mortars into Turkish border towns over the past two days, including Akcakale, killing at least six civilians including a nine-month-old boy.
On the Syrian side, seven civilians and eight Kurdish fighters have been killed since the operation began, according to activists.
A Kurdish-led group and Syrian activists said that despite the bombardment, Turkish troops had not made much progress on several fronts they had opened. But their claims could not be independently verified.
Turkish President Recep Tayyip Erdogan said 109 "terrorists" were killed in the offensive, a reference to the Syrian Kurdish fighters. But reports from the area did not indicate anything remotely close to such a large number of casualties.
Mr Erdogan also warned the European Union not to call Ankara's incursion into Syria an "invasion", and renewed a threat to "open the gates" and let Syrian refugees flood into Europe.
Turkish Foreign Minister Mevlut Cavusoglu said the military intends to move 19 miles into northern Syria and that its operation will last until all "terrorists are neutralised".
Meanwhile, the Kurdish forces have halted all operations against IS in order to focus on fighting Turkish troops.
Ankara considers members of the Kurdish militia to be "terrorists" because of their links to the outlawed Kurdistan Workers' Party, or PKK, which has led an insurgency against Turkey for 35 years.
Turkey, a Nato member, considers its operations against the Kurdish militia in Syria a matter of its own survival, and it also insists it will not tolerate the virtual self-rule that the Kurds succeeded in carving out in northern Syria along the border.
The Turkish assault aims to carve out a corridor of control along the length of the border - a so-called "safe zone" - clearing out the Kurdish militia.
Such a zone would end the Kurds' autonomy in the area and put much of their population under Turkish control. Ankara has said it aims to settle two million Syrian refugees, who are mainly Arabs, in the zone.
Turkey began its offensive in northern Syria on Wednesday with air strikes and artillery shelling, and then ground troops crossed the border later in the day.
Mustafa Bali, a spokesman for the Kurdish-led Syrian Democratic Forces, said their fighters have repelled Turkish forces ground attacks. "No advance as of now," he tweeted on Thursday.
But Major Youssef Hammoud, a spokesman for Turkish-backed opposition fighters participating in the operation, said they captured the village of Yabisa, near Tal Abyad.
Turkey's state-run news agency said the allied Syrian fighters had cleared and entered a second village, Tel Fander, but provided no details. The Britain-based Syrian Observatory for Human Rights said Turkish commandos had entered the village of Beir Asheq.
The Observatory said more than 60,000 people have fled their homes since Wednesday, while the UNHCR estimated it at tens of thousands.
It called on parties to adhere to international humanitarian law, including providing access for aid agencies, and warned of an escalating humanitarian crisis among Syrian civilians.
The UN Security Council failed to agree on a statement following a closed meeting on Turkey's operation.
The five European council members who called the meeting urged Turkey in a joint statement afterwards "to cease the unilateral military action".
The UK, France, Germany, Belgium and Poland warned that "renewed armed hostilities in the north-east will further undermine the stability of the whole region, exacerbate civilian suffering and provoke further displacements".
