Human Rights Watch said Tuesday that "unidentified projectiles" launched by Yemen's Huthi rebels caused a March 7 blaze that killed dozens of migrants at a holding facility in the capital.

The Iran-backed rebels control much of northern Yemen, including the capital Sanaa, whose capture from the Saudi-backed government in 2014 sparked a devastating war.

"Scores of migrants burned to death in Yemen on March 7, 2021, after Huthi security forces launched unidentified projectiles into an immigration detention centre in Sanaa, causing a fire," HRW said in a statement.

It said detainees -- most of them Ethiopian migrants -- had been protesting against overcrowding when camp guards rounded up hundreds of them into a hangar and fired two projectiles into the building.

"The migrants said the first projectile produced a lot of smoke and made their eyes water and sting. The second, which the migrants called a 'bomb', exploded loudly and started a fire," HRW said.

Footage that AFP obtained from one of the survivors showed dozens of charred bodies piled on top of one another and strewn across the ground, with one person crying out in prayer.

Another video published by HRW showed security forces walking among survivors outside the facility, as the fire raged inside with black smoke billowing.

HRW said hundreds of injured migrants were being treated in hospitals in Sanaa where a "heavy security presence" had posed problems for humanitarian agencies.

It cited interviewees as saying they saw the Huthis rearrest migrants who were not severely injured.

"Huthi authorities should urgently engage with Ethiopian authorities whose nationals are languishing in Yemeni detention centres under their control," HRW said.

- 'I was terrified' -

Last week, the International Organization for Migration urged the rebels to provide unimpeded access to the injured.

It said more than 170 people had been hurt, over half of them seriously, and cited local migrant groups as saying as many as 60 people were killed.

"I don't have the words to express what it was like - (the projectiles) exploded, and there was so much smoke and then there was a fire that spread," HRW quoted a 20-year-old migrant as saying.

"I was terrified, I felt like my mind was blocked with smoke."

In correspondence with HRW, Huthi spokesman Mohammed Abdulsalam said the incident "should not be politicised or exploited".

"The incident that took place was a normal result that occurs in similar incidents all over the world," he said, according to the statement.

He called for the lifting of a longstanding Saudi-led blockade on Sanaa's rebel-controlled airport, so migrants "can return home".

The Saudi-led coalition intervened in Yemen in 2015 to back the government against the rebels. Since then, tens of thousands have been killed and millions displaced in what the United Nations calls the world's worst humanitarian crisis.

Despite more than six years of conflict, the impoverished country is still a magnet for migrants from the nearby Horn of Africa seeking a better life in the wealthy Gulf Arab states.