Syrian Kurdish mother Shara Sido says the news came to her through a messaging application.

Ms Sido, 65, received an image of a bullet-riddled corpse with the instruction: "Come collect your son."

Sitting inside a modest house in the de facto Syrian Kurdish capital of Qamishli, the displaced woman scrolls through her phone to find a picture.

"This is the monster," she says, showing a photo of the Syrian fighter she claimed confessed to shooting dead her son, 38.

"They killed my son in cold blood," she told AFP, blaming Turkey-backed Syrian fighters.

Turkish troops and their Syrian proxies have overrun a strip of northern Syria since October, after a deadly military campaign against Kurdish forces that led tens of thousands to flee their homes.

Rights groups and displaced Kurdish families have accused the Syrian rebels of executions, home confiscations and looting in the border area, charges the fighters deny.

Ms Sido lived in the border town of Ras Al Ain before Turkey and its rebel proxies on October 9 launched an offensive against Kurdish forces they consider to be terrorists.

As soon as the invasion started, the mother of five and her family fled to Qamishli, carrying nothing but a few basic items.

Her son, Rezan, returned to Ras Al Ain one week later to collect personal documents and clothes for his three children, but rebels stopped him, Ms Sido said.

They fired bullets at his vehicle, killing him along with a driver and three of his friends, she said, showing pictures of bullet wounds on their corpses.

"I will expose their crimes to the world," Ms Sido said.

Such stories have instilled fear in the Kurdish minority, who have long accused Turkey of trying to force them out.

"They are coming to kill the Kurds," Ms Sido said after the latest cross-border incursion.

In the two months since the invasion started, Turkey has established a "safe zone" in a 120-kilometre long strip along its southern border, where it says it wants to resettle Syrian refugees.

Turkish state media last month said about 70 Syrians, including women and children, crossed the border to Ras Al Ain in the first of the returns.

Meanwhile, the UN says about half of the 200,000 people displaced by the military operation are starting to return to the area.

But the Syrian Observatory for Human Rights says most of those returning are Arabs, not Kurds.

Mustafa Al Zaim, a Kurdish merchant who fled to Qamishli in October, said there was no way he was going back.

"We wouldn't even think of returning without international guarantees," said Mr Al Zaim, 44.

He said Turkey-backed rebels had seized his home, a supermarket and several other stores he owned in Ras Al Ain.

They also sent him a message asking for $15,000 to "protect" his property and stock, an offer he said he refused.

"They had already robbed and looted everything," Mr Al Zaim said.

In a recent report, Human Rights Watch said the rebels barred Kurdish families from returning to Turkey's zone, while looting and occupying property they left behind.

Sarah Leah Whitson, the organisation's Middle East director, accused Turkey of "turning a blind eye to the reprehensible behaviour displayed by the factions it arms".

Ms Whitson said that "as long as Turkey is in control of these areas, it has a responsibility to investigate and end these violations".

The Syrian National Army, an alliance of Turkey-backed rebel groups, on Saturday denied the accusations.

It called on the rights group to withdraw the "biased" report, saying it "does not reflect reality".

Turkey's invasion was the latest in a series of such military operations on Syrian soil.

Early last year, pro-Ankara fighters seized the north-west region of Afrin from Kurdish combatants, with rights groups reporting similar abuses in that region.