Saudi border guards are accused of the mass killing of migrants along the Yemeni border in a new report by Human Rights Watch.
The report says hundreds of people, many of them Ethiopians who cross war-torn Yemen to reach Saudi Arabia, have been shot dead.
Migrants have told the BBC they had limbs severed by gunfire and saw bodies left on the trails.
Saudi Arabia has previously rejected allegations of systematic killings.
The Human Rights Watch (HRW) report, titled They Fired On Us Like Rain, contains graphic testimony from migrants who say they were shot at and sometimes targeted with explosive weapons by Saudi police and soldiers on Yemen’s rugged northern border with Saudi Arabia.
Migrants contacted separately by the BBC have spoken of terrifying night-time crossings during which large groups of Ethiopians, including many women and children, came under fire as they attempted to cross the border in search of work in the oil-rich kingdom.
“The shooting went on and on,” 21-year-old Mustafa Soufia Mohammed told the BBC.
He said some in his group of 45 migrants were killed when they came under fire as they tried to sneak across the border in July last year.
“I didn’t even notice I was shot,” he said, “but when I tried to get up and walk, part of my leg was not with me.”
The remoteness of the border crossings and the difficulty of tracking down survivors make it impossible to know precisely how many people have been killed, say the authors.
“We say a minimum of 655, but it’s likely to be thousands,” Hardman said. “We have factually demonstrated that the abuses are widespread and systematic and may amount to a crime against humanity,” she said.
Reports of widespread killings perpetrated by Saudi security forces along the northern border first surfaced last October in a letter by UN experts to the government in Riyadh.
They highlighted “what appears to be a systematic pattern of large-scale, indiscriminate cross-border killings, using artillery shelling and small arms fired by Saudi security forces against migrants.”
Despite the horrific nature of the allegations, the letter went largely unreported.
The Saudi government said it took the allegations seriously but strongly rejected the UN’s characterization that the killings were systematic or large-scale.
“Based on the limited information provided,” the government replied, “authorities within the Kingdom have discovered no information or evidence to confirm or substantiate the allegations.”
But last month, the Mixed Migration Centre, a global research network, published further allegations of killings along the border, based on its interviews with survivors.
Its report contains graphic descriptions of rotting corpses scattered throughout the border area, captured migrants being asked by Saudi border guards which leg they want to be shot through, and machine guns and mortars being used to attack large groups of terrified people.
The report from Human Rights Watch is the most detailed yet, with multiple eyewitness reports and satellite imagery of the crossing points where many of the killings are said to have taken place, as well as makeshift burial sites.
The report also identifies a detention center at Monabbih, just inside Yemen, where migrants are held before being escorted to the border by armed smugglers.
According to one migrant interviewed by HRW, Yemen’s Houthi rebels are in charge of security at Monabbih and work alongside the smugglers.
A satellite photo shows bright orange tents packed closely together inside a fenced-off compound.
While the HRW report covers events up to June this year, the BBC has uncovered evidence that the killings are continuing.
In the northern city of Saada, footage seen by the BBC shows migrants injured at the border arriving in a hospital as late as Friday. In a nearby cemetery, burials were taking place.
The BBC has approached the Saudi government for comment about the allegations made by UN rapporteurs, the Mixed Migration Centre, and Human Rights Watch, but has not received a response.