The report, now in the hands of the UN Security Council, does not identify the supplier of the weaponry but says missile debris inspected by UN experts was of Iranian origin.
A UN panel of experts wrote the report examining if a Security Council arms embargo imposed on Yemen was being broken. Portions of the report were shared with CNN by two different UN diplomats who declined to be identified since the report has not been officially released.
The report also criticizes Saudi Arabia and its coalition fighting the Iranian-backed rebels in Yemen for not doing enough to prevent civilian casualties.
However, a significant portion of the report blames Iran and could be used to justify further action by the US, which has blasted the Iranians on several fronts and accused of them of arming rebels in Yemen with ballistic missiles.
The report comes days after President Donald Trump avoided upending the nuclear deal with Iran that he has repeatedly disparaged, agreeing to waive key sanctions the US lifted as part of the deal.
The report says: "The Panel has identified missile remnants, related military equipment and military unmanned aerial vehicles that are of Iranian origin and were introduced into Yemen after the imposition of the targeted arms embargo. As a result, the Panel finds that the Islamic Republic of Iran is in non-compliance with paragraph 14 of resolution 2216 (2015) in that it failed to take the necessary measures to prevent the direct or indirect supply, sale or transfer, of Borkan-2H short-range ballistic missiles, filed storage tanks for liquid bi-propellant oxidizer for missiles and Ababil-T (Qasef-1) unmanned aerial vehicles, to the then Houthi-Saleh alliance."
Iran has steadfastly denied accusations it is arming the Houthis and charged US Ambassador to the UN Nikki Haley with fabricating evidence after the diplomat held an event
in a US military hangar to demonstrate Iran made a missile that was fired at Riyadh airport in November. A request to the Iranian mission to the UN for comment has not been answered.
Yemen is described by the UN as the world's worst humanitarian crisis. Over 10,000 people have been killed in the three years of war, an estimated 7 million are on the brink of famine, and one million people are threatened by an outbreak of cholera.
The country has been become the center of a proxy war between regional powers Iran and Saudi Arabia. The report states there is "no evidence" that either side did anything "to mitigate the devastating impact" of attacks on the civilian population. The UN experts traveled to Saudi Arabia late last year to examine remnants from Houthi missile firings into Saudi Arabia.
The new UN report now being studied by council diplomats states that after the years of war Yemen 'has all but ceased to exist". For months, humanitarian aid has been blocked by the Saudi coalition. The report states the Saudi coalition was using 'the threat of starvation as a bargaining tool and an instrument of war".
The experts examined the impact of Saudi coalition attacks inside Yemen and focused on ten air strikes which killed hundreds of people. The report said "measures taken by the Saudi-led coalition in its targeting process to minimize child casualties if any, remain large ineffective".
Cranes to help aid arrives
On Monday, Haley said four US supported cranes had reached the port of Hudaydah in Yemen. She said the cranes would be used to improve the ports capacity for offloading badly needed supplies, such as food and medicine. Haley said "no one should ever have to live the way the people of Yemen are living".
The UN welcomed the arrival of the cranes. UN spokesman Stephane Dujarric told reporters in New York "the problem that we've had is that the facilities in the port did not enable us to offload and to absorb a greater capacity of ships. But it's an obviously important development and we've been waiting and more importantly the people of Yemen have been waiting for the arrival of these cranes for some time".
But as the war rages on the UN report strikes a pessimistic note. The panel says "all parties to the conflict continue to believe that they can achieve a military victory that would negate the necessity for political compromise" The 79 page report adds "political decision makers on all sides are not bearing the brunt of war. Yemeni civilians are."