Airstrikes by suspected Turkish jets on a Kurdish village in northern Syria killed at least 19 civilians, a monitoring group and Kurds said on Wednesday.
The dead included three children in the overnight attack on the village of Thalthana, located north-west of the Islamic State-controlled town of al-Bab, the Syrian Observatory for Human Rights added.
The Kurdish Hawar News Agency blamed Turkish and US-led warplanes for the attack, saying it also injured 100 civilians.
There was no comment from Ankara or Washington.
Turkey invaded northern Syria in August to attack Islamic State and Kurdish militants, though in recent weeks it has turned its focus on the jihadist group, after the United States urged Ankara, its NATO-ally, to refrain from further attacks on the Kurds.
The US has allied with the Syrian Kurds against Islamic State since 2014 and together seized most of the territory the extremist group held along the Turkish border.
A Turkish soldier was killed and three injured in clashes just over the border, against Islamic State militants, Turkey's state-run Anadolu news agency reported on Wednesday.
Anadolu also claimed 18 Islamic State militants were "neutralized" in the clashes, which is edging closer to Dabiq, a small town.
In jihadist eschatology, Dabiq holds great symbolic value as a site of a key war. Islamic State named its English-language magazine Dabiq.
Turkish soldiers are fighting alongside Syrian rebel forces.
In recent weeks, violence has escalated in several fronts in war-wracked Syria.
Later Wednesday, officials from Germany, France, Britain, Italy and the United States are due to hold talks in Berlin on the situation in Syria.
"We must find ways to finally end this madness, this killing and dying in Syria," German Foreign Minister Frank-Walter Steinmeier said in Brussels, where he was attending an international conference on Afghanistan, before returning to Berlin for the talks.
Besides Steinmeier, no other foreign ministers are expected at the Berlin talks, which will take place at the level of political directors.
Syria has seen a surge in fighting since a ceasefire brokered by the US and Russia collapsed last month, a week after it went into effect on September 12.
The northern divided city of Aleppo has since been a major battleground between government forces, backed by Russian air power, and rebels.
United Nations experts said Wednesday that an attack on an aid convoy that killed more than 20 civilians last month near Aleppo was definitively from an airstrike.
"I can verify that the convoy was bombed," said Lars Bromley of the UN satellite observation programme UNOSAT. "In our analysis, we saw that it was an airstrike."
Bromley added the findings were based on satellite images provided to the UN by the US State Department but provides no information as to who was behind the airstrike.
However, the Observatory’s head, Rami Abdel-Rahman, suspected Russian involvement.
“I have information that Russian planes carried out the attack," he told dpa without giving details.
The September 19 airstrike shattered the truce and triggered a bitter row between Washington and Moscow as to who stood behind the attack.