UNITED NATIONS (Reuters) - U.N. investigators accused a Saudi Arabia-led military coalition of carrying out a deadly March attack on a Somali migrant boat off Yemen and said the alliance had become a cover for some states to avoid individual blame, according to a confidential report seen by Reuters on Wednesday.

Somali refugees who survived an attack on a boat off Yemen's coast in the Red Sea hug each other as they sit at a detention center in the Houthi-held port of Hodeidah, Yemen, March 22, 2017. Picture taken March 22. REUTERS/Abduljabbar Zeyad

The coalition fighting the Iran-allied Houthi militia in Yemen has denied striking the boat in the Red Sea near the port of Hodeidah. The investigators said the attack killed 42 people and injured 34 of the more than 140 people onboard.

“This civilian vessel was almost certainly attacked using a 7.62 mm caliber weapon from an armed utility helicopter,” the investigators, who monitor sanctions in Yemen, wrote in a 185-page report to the U.N. Security Council on Monday.

“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,” the report said. It said the helicopter was likely operating from a naval vessel.

The coalition intervened in Yemen in 2015 in support of the internationally recognized government of President Abd-Rabbu Mansour Hadi. It includes Egypt, the United Arab Emirates, Bahrain, Kuwait, Jordan, Morocco, Senegal and Sudan.

The U.N. report said the attack violated international humanitarian law and threatened the peace, security and stability of Yemen.

It said two other alleged attacks on fishing vessels by helicopter or naval vessels in the Red Sea in March had killed another 11 people and injured eight.

It said the Saudi-led coalition, the governments of the UAE and Egypt and the Combined Maritime Forces had not responded to the investigators’ requests for information.

The coalition receives U.S. arms and logistical support.

“Some individual member states of the Saudi Arabia-led coalition seek to hide behind ‘the entity’ of the coalition to shield themselves from state responsibility for violations committed by their forces,” the investigators said.

They did not identify the states by name.

“Attempts to divert responsibility in this manner from individual states to the Saudi Arabia-led coalition may contribute to further violations continuing with impunity,” they wrote.

Top U.N. officials this month accused the warring parties in Yemen and their international allies of fueling an unprecedented deadly cholera outbreak, driving millions closer to famine and hindering humanitarian aid access.

U.N.-led peace talks have stalled. At U.S. Ambassador Nikki Haley’s suggestion, the Security Council is considering sending letters to the warring parties reminding them of their humanitarian obligations.

The letter has to be agreed by consensus and Egypt has objected to the draft, said a senior council diplomat who spoke on condition of anonymity, adding that negotiations were continuing.