The attack on the boat, believed to be carrying 145 people leaving Yemen, was among the most horrific episodes of deadly violence on asylum seekers there since Saudi Arabia and its allies entered the country’s civil war and began an air campaign against the Houthi rebels two years ago.
The boat assault also illustrated the vibrant trade in people-smuggling between the Horn of Africa and Yemen, a congregation point for tens of thousands of Africans fleeing their own countries.
Most of the passengers aboard the vessel were believed to be Somalis who had been staying in Yemen and were trying to reach Sudan.
Filippo Grandi, the United Nations high commissioner for refugees, described the assault as an “unwarranted attack on helpless civilians fleeing violence and conflict” in a statement from the refugee agency’s Geneva headquarters.
“Many questions remain unanswered on the circumstances of this horrific event,” Mr. Grandi said. “We call on all parties to the conflict to make proper inquiries to ensure accountability and to prevent this from happening again.”
Officials in Yemen initially said forces of the Saudi-led coalition had been responsible for the attack, which occurred on Friday about 30 miles from the western Yemen port of Al Hudaydah.
Saudi officials denied responsibility, saying none of the coalition’s forces had been operating in the area. They also said Al Hudaydah should be placed under United Nations supervision, describing it as a conduit for weapons smuggling and people-smuggling.
On Saturday the government of Somalia, which is a member of the Saudi coalition, also called for an investigation.
Accounts from survivors and crew described an unprovoked predawn attack by a military helicopter, as passengers screamed “We are Somali!” and held flashlights aloft to show they posed no threat. By then, many were already dead.
The captain, who was fatally wounded, was able to pilot the boat to Al Hudaydah, where rescue workers stored the dead in fish coolers because hospitals had no room, the head of port security said.
Yemen, the poorest country in the Middle East, has been consumed by war since March 2015 when Saudi Arabia and its partners began bombarding the Houthis, who had seized parts of the country including the capital, Sana, from the government. The Saudis have accused Iran, their regional rival, of arming the Houthis, who are from the north of Yemen.
The war has created a humanitarian disaster that has displaced millions of Yemenis and put many at risk of famine.