Women and children are among at least 42 Somali refugees who died after their boat was sacked at from a helicopter in Yemen, the International Organisation for Migration says.
The UN Refugee Agency (UNHCR) said it was "deeply distressed" by the casualties and called for all parties in the Yemeni civil war to protect civilians in accordance with worldwide law.
It was not clear who carried out the attack.
Al-Massirah Yemeni television reported that the Saudi-led warplanes targeted a boat carrying dozens of Somali immigrants off al-Hudaydah in Yemen.
Some survivors said they believed they.
The refugees were hit by light weapons fire in waters off rebel-held Hodeida but managed to dock in the city's port, an official there said.
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The Saudi-led and USA -backed coalition began striking the rebels and their allies in March 2015, hoping to drive the Houthis from the capital, Sanaa, and restore the internationally recognized government. 32 people, including 10 civilians, have been killed.
Some of the area around the strait is controlled by Houthi rebel fighters, who overrun Yemen's capital Sanaa in 2014 and forced the Saudi-backed president, Abed Rabbo Mansour Hadi, to flee into exile in Saudi Arabia.
The medical official said the bodies of the dead were being retrieved from the sea and taken to the morgue of a hospital in al-Thawra.
"The attack took place in the Red Sea off Yemen, late Thursday", IOM spokesman Joel Millman told a news conference in Geneva. It did not say who was behind the airstrike.
A sailor who had been operating the boat, Ibrahim Ali Zeyad, said 80 refugees had been rescued after the incident. The coalition is the only party to the conflict with naval and air forces, and rights groups have documented hundreds of airstrikes in which civilians have been killed.
African migrants continue to head to Yemen, a transit point to Saudi Arabia where they seek jobs and a better life. It also said that the dead included women and children.