Thirty-one Somali refugees were killed off the coast of Yemen late on Thursday when a helicopter attacked the boat they were travelling in, a local coast guard in the Houthi-controlled Hodeidah area said.
Coast guard Mohamed al-Alay told Reuters the refugees, carrying official UNHCR documents, were on their way from Yemen to Sudan when they were attacked by an Apache helicopter near the Bab al-Mandeb strait.
A sailor who had been operating the boat, Ibrahim Ali Zeyad, said 80 refugees had been rescued after the incident.
It was not immediately clear who carried out the attack.
Hodeidah on the Red Sea is controlled by Iran-allied Houthi fighters who in 2014 overran Yemen's capital Sanaa and forced the Saudi-backed government of President Abd-Rabbu Mansour Hadi to flee into exile.
A Saudi-led coalition was formed in 2015 to fight the Houthis and troops loyal to former President Ali Abdullah Saleh who have fired missiles into neighbouring Saudi Arabia.
The Bab al-Mandeb is a strategic waterway at the foot of the Red Sea through which nearly 4 million barrels of oil are shipped daily to Europe, the United States and Asia.