Human Rights Watch said Tuesday that "unidentified projectiles" launched by the Iran-backed Houthi militias in Yemen caused a March 7 blaze that killed dozens of migrants at a holding facility in the capital. "Scores of migrants burned to death in Yemen on March 7, 2021, after Houthi security forces launched unidentified projectiles into an immigration detention center in Sanaa, causing a fire," HRW said in a statement. It said inmates -- 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. It added that hundreds of injured inmates were being treated in hospitals in Sanaa where a "heavy security presence" had posed problems for humanitarian agencies. Last week, the International Organization for Migration urged the Houthis to provide unimpeded access to the injured. It said more than 170 people had been hurt, over half of them seriously, and as many as 60 killed. Despite more than six years of conflict, the impoverished country is still a magnet for migrants from the nearby Horn of Africa.