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."
It was a brutal, chaotic end to a three-month journey fraught with danger, starvation and violence at the hands of Yemeni and Ethiopian smugglers.
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A video filmed hours later shows his left foot almost completely severed. Mustafa's leg was amputated below the knee and now, back with his parents in Ethiopia, he walks with crutches and an ill-fitting prosthetic limb.
"I went to Saudi Arabia because I wanted to improve my family's life," the father-of-two said, "but what I hoped for didn't materialise. Now my parents do everything for me."
'Killing fields'
Some survivors show signs of deep trauma.
In the Yemeni capital, Zahra can barely bring herself to speak about what happened.
She says she is 18, but looks younger. We are not using her real name to protect her identity.
Her journey, which had already cost around $2,500 (£1,950) in ransoms and bribes, ended in a hail of bullets at the border.
One bullet took all the fingers of one hand. Asked about her injury, she looks away and cannot answer.
