T hey left the northern Syrian city of Qamishli in a convoy of buses, motorbikes and cars. Men and women, young and old. They sang songs and flashed peace signs as they passed slowly through towns and villages along the way.

The convoy of Kurdish protesters was heading to Ras al-Ayn, a border town that had seen days of heavy fighting between the Turkish military and Kurdish forces.

They planned to show their opposition to Turkey’s military operation with a symbolic demonstration, and then leave. But many of them never made it back.

At around 4pm on Sunday, shortly after they arrived in the city, a large group of people was hit in what is believed to be a Turkish airstrike or artillery attack as they stood outside their vehicle at the front of the convoy. Twelve people were killed, most of them civilians. Among them were two journalists who were there to cover the protest. A further 70 people were injured.

The incident, coming just days into Turkey’s highly controversial incursion into northern Syria, may be the first recorded war crime by the Nato power since the start of the offensive.

Turkey launches offensive into Syria Show all 25 1 /25 Turkey launches offensive into Syria Turkey launches offensive into Syria Turkish soldiers with armored vehicles EPA Turkey launches offensive into Syria A woman flees with her children during Turkish bombardment on Syria's northeastern town of Ras al-Ain AFP/Getty Turkey launches offensive into Syria Smoke billows following Turkish bombardment on Syria's northeastern town of Ras al-Ain in the Hasakeh province along the Turkish border on October 9, 2019. - Turkey launched an assault on Kurdish forces in northern Syria with air strikes and explosions reported along the border. President Recep Tayyip Erdogan announced the start of the attack on Twitter, labelling it "Operation Peace Spring". (Photo by Delil SOULEIMAN / AFP) (Photo by DELIL SOULEIMAN/AFP via Getty Images) DELIL SOULEIMAN AFP/Getty Turkey launches offensive into Syria The first group of Turkish infantry prepare to enter Syria on the border Getty Turkey launches offensive into Syria Civilians flee AFP/Getty Turkey launches offensive into Syria Smoke billows from targets inside Syria AP Turkey launches offensive into Syria Turkish armoured vehicles enter Syria in Akcakale Getty Turkey launches offensive into Syria Civilians leave as smoke rises from Ras al-Ain AFP Turkey launches offensive into Syria A multi-rocket launcher fires in an unknown location Turkish Defence Ministry via Reuters Turkey launches offensive into Syria People wave as Turkish soldiers prepare to cross the border Getty Turkey launches offensive into Syria Girls stand together in Ras al Ain town Reuters Turkey launches offensive into Syria A woman walks as smoke billows following Turkish bombardment in Syria's northeastern town of Ras al-Ain AFP/Getty Turkey launches offensive into Syria A Turkish army's tank drives down from a truck towards the border with Syria AFP/Getty Turkey launches offensive into Syria Turkish jet taxis on tarmac after returning to a military base in southeast Diyarbakir Reuters Turkey launches offensive into Syria A Turkish armored vehicle drives down a road during a military operation in Kurdish areas of northern Syria EPA Turkey launches offensive into Syria People sit on belongings at a back of a truck as they flee Ras al Ain town Reuters Turkey launches offensive into Syria Turkey-backed Syrian opposition fighters enter Tel Abyad AFP/Getty Turkey launches offensive into Syria Civilians flee AFP/Getty Turkey launches offensive into Syria People flee Tal Abyad North Press Agency/Reuters TV Turkey launches offensive into Syria People wave as Turkish soldiers prepare to cross the border into Syria Getty Turkey launches offensive into Syria Civilians flee with their belongings AFP/Getty Turkey launches offensive into Syria Civilians flee during Turkish bombardment on Syria's northeastern town of Ras al-Ain in the Hasakeh province along the Turkish border on October 9, 2019. - Turkey launched a broad assault on Kurdish-controlled areas in northeastern Syria today, with intensive bombardment paving the way for an invasion made possible by the withdrawal of US troops. (Photo by Delil SOULEIMAN / AFP) (Photo by DELIL SOULEIMAN/AFP via Getty Images) DELIL SOULEIMAN AFP/Getty Turkey launches offensive into Syria Turkish President Recep Tayyip Erdogan, right, speaks with Defense Minister Hulusi Akar, left, as they watch the operation by Turkish forces in Kurdish areas EPA Turkey launches offensive into Syria Smoke rises from the Syrian town of Tal Abyad AFP/Getty Turkey launches offensive into Syria Turkey-backed members of Syrian National Army prepare for moving to Turkey with heavy armed vehicles EPA

As video evidence has emerged in the last few days, Amnesty International said its own investigation found that the attack constituted a war crime.

“The convoy attack is one of the most horrific incidents that’s taken place in the past few days,” said Lynn Maalouf, Amnesty’s Middle East research director. “Amnesty verified the imagery and corroborated with witness testimony – and concluded that this attack clearly violated international humanitarian law.

“There is nothing safe about this zone that Turkey claims it wants to create – so far, its actions and those of its allies on the ground just demonstrate their utter disregard for civilian lives.”

The Independent understands the United Nations is also investigating the incident to determine if it constituted a war crime.

The war has already killed around 80 civilians in Syria and injured more than 400. Over 300,000 people have been displaced by the fighting so far. Turkish authorities said at least 18 civilians have been killed in Turkey by mortar fire from Kurdish forces.

The international community has widely condemned the offensive, which was sparked when Donald Trump withdrew US troops from the Syria-Turkey border, effectively giving Ankara a green light to attack the Kurdish-led Syrian Democratic Forces.

Video shows moments before Turkish airstrike on civilian convoy

The details of what happened on Sunday have emerged slowly. The good spirits of the protesters belied the obvious danger they were in as they made their way to Ras al-Ayn. They were heading towards an active warzone, to a city that was being pummelled by airstrikes and artillery. The presence of a small number of armed men in the convoy made the journey even more perilous.

And yet, international investigators have told The Independent they believe it would have been unlikely for Turkey – a country with an advanced drone programme, and with the sophisticated surveillance that provides – to mistake the convoy for a military target. Videos of previous strikes released by the Turkish military show the clarity of view provided by its aircraft.

The Turkish military would have seen the convoy make its way slowly along the road for more than 80 miles, stopping along the way. In the town of Tell Tamr, more people joined. It was large and visible. They would have seen many women in the group.

“You might have thought they were going to a wedding, not a war,” said Lindsey Hilsum, a journalist for Channel 4 News, in her dispatch from along the convoy’s route, shortly before it was hit.

One protester was asked whether she was afraid. She replied: “We’re not scared of fighting. Erdogan has been threatening us for eight years, but we’re not afraid.”

When they reached the city of Ras al-Ayn, perhaps more than 100 people had joined in dozens of minibuses. They stopped in a street lined with shuttered shops, where they stepped out.

They had purposefully chosen a point in the centre of the city to hold their protest, away from the fighting to the west and the east.

One video shows the group dancing and singing, somewhat nervously. Another video shows what appears to be the same group gathering. There is a loud bang and a bright flash, followed by darkness. Another video posted online shows the gruesome aftermath of the strike. Bodies lie scattered on the floor while survivors sit up dazed and burned.

A witness later said they did not hear jets in the sky prior to the bombing, which suggests that the explosion could have been caused by artillery or a drone attack, rather than an airstrike. Investigations are now under way to discover the type of munition used.

Images posted online show some of the dead appeared to be holding guns. The Syrian Observatory for Human Rights said at least nine people were killed, including five civilians. Kurdish authorities put the number at 12 killed and 74 injured, but did not say how many were civilians.

Smoke rises from the Syrian town of Ras al-Ayn after an attack on Wednesday (AFP/Getty)

An elderly mother of two named Dayika Akide was among the dead, according to local reports. Mohammed Hussein Rasho, a Syrian Kurdish reporter and cameraman for Cira TV, was injured in the blast and died of his wounds the following day, according to the Committee to Protect Journalists. Syrian Kurdish journalist Saad Ahmed, a reporter for the local news agency Hawar News, was also killed in the strike.

The United Nations Office for the Coordination of Humanitarian Affairs said on Tuesday that the strike the “worst incident we are aware of so far”, in the conflict.

The Middle East and North Africa representative of the Committee to Protect Journalists, Ignacio Miguel Delgad, said: “Judging by the evidence we have, the footage and pictures we have seen and testimonies from eyewitnesses, it was clearly a civilian convoy on their way to Ras al-Ayn to protest the Turkish offensive.

“International law expressly prohibits attacks on civilians and journalists. CPJ believes this airstrike could constitute a war crime and we call on Turkish authorities to immediately cease their attacks on journalists and civilians.”

Further investigations are now likely to focus on whether the attack meets the conditions to be a breach of international humanitarian law. That process can be extremely complicated.

“There are certainly elements here that could lead you to conclude that they knew it was not a military objective,” William Schabas, professor of international law at Middlesex University in London, told The Independent.

He said: “There is a burden on the person who drops the bomb to take reasonable efforts to make sure they know the answer to the question about whether the target is military, and even if it is, whether there is an acceptable level of collateral damage to non-combatants.

“This case is complicated by the fact that there were armed people with the convoy. It’s not implausible Turkey would say it has a military dimension.”

Professor Schabas added that much of how the investigation proceeds will depend on how Turkey responds, or if it responds at all.

“Let’s assume we don’t get a credible explanation from Turkey, we still have to reach conclusions of whether there was a war crime,” he said.