“The Saudi Arabia-led coalition forces are the only parties to the conflict that have the capability to operate armed utility helicopters in the area,” it added.

The gunfire went on for five minutes. When it was over, 42 people were dead, and 34 more were wounded. The attackers made no efforts to help the victims. It took the boat six hours to reach safety. Neither Saudi Arabia nor the United Arab Emirates, which has naval forces in the area, cooperated with the panel, the report said, accusing them of “obstruction.” Nor did the Houthis, the rebels who have seized part of Yemen, give the panel access to the port of Al Hudaydah, which they control, to interview survivors and examine evidence.

No one has claimed responsibility for the attack.

The report, written by a four-member panel of experts and expected to be discussed by Council members on Monday, was seen by The New York Times on Wednesday. It is unclear whether the Council will take any action. Both Britain and the United States, permanent members of the Council, support the Saudi-led military coalition.

The report paints a harrowing picture of what happened on the night of March 16 as a boat packed with up to 145 people, mostly Somalis, was sailing across the Red Sea, away from the Yemeni coast. The panel said it found no evidence of fighters or weapons on the vessel.

A large ship approached their boat and ordered it to stop. When it did not, the attack began. First, rockets were fired, and then, sustained gunfire from either a “medium machine gun or minigun of 7.62 mm caliber mounted on a helicopter,” according to the report.