But the report also had harsh words for Saudi Arabia and the United Arab Emirates, two of the Trump administration's closest Arab allies, saying they have continued or expanded their support for Yemeni forces that undermine the authority of the government and could hasten the fragmentation of the state.
The U.N. experts were particularly critical of airstrikes by the Saudi-led coalition. The U.N. previously had said that the majority of the more than 5,000 civilian deaths in the conflict were a result of the airstrikes, which are carried out by a handful of coalition countries including Saudi Arabia and the United Arab Emirates, often using U.S.-supplied munitions.
The report, which has not yet been made public, was obtained by The Washington Post.
The panel's findings, nearly three years after the eruption of widespread hostilities in Yemen, add weight to repeated warnings by aid workers and analysts about the risks of a humanitarian catastrophe, rampant human rights abuses and the potential for the battle to spill over Yemen's borders.
With the proliferation of local rivalries and armed groups with competing loyalties, "Yemen as a state has all but ceased to exist," the report said.
What began as a largely domestic fight after the Houthi rebels seized control of Sanaa, the capital, and drove the government from power has been transformed into an arena for the regional feud between Iran and Saudi Arabia. The Saudi-led coalition, which receives military support from the United States, entered the war in 2015 to restore the government and dislodge the Houthis, whom the Saudis accused of acting as an Iranian proxy force, a charge the Houthis have long denied.
Eight million people, or a third of Yemen's population, are facing famine. A cholera outbreak that has affected roughly a million people is one of the largest ever recorded. More than 10,000 people have been killed since the war began.
Houthi missile attacks in recent months targeting Saudi Arabia — including one that reached the Saudi capital — have raised fears that the war could spark a wider regional conflict. The United States and the Saudis have accused Iran of supplying ballistic missiles to the Houthis, while arguing that the weapon transfers are proof of Iran's destabilizing role in the region.
The Iranian government has denied providing the Houthis with weapons.
At least four attacks on Saudi Arabia were carried out with missiles capable of a range "beyond that normally expected of the known missiles" in the Houthi arsenal, the panel said. The U.N. panel examined the remnants of two of the missiles — fired July 22 and Nov. 4 — and found that they were consistent with the design of an Iranian missile and "almost certainly produced by the same manufacturer."
While the report criticized Iran for failing to halt the transfer of weapons, the panel could not say with certainty how they were transported to the Houthis or who the supplier was.
In reviewing the conduct of Saudi-led military activity, the U.N. panel examined 10 airstrikes last year that killed 157 people, including 85 children, and found that "measures taken by the Saudi Arabia-led coalition in its targeting process to minimize child casualties, if any, remain largely ineffective." And a coalition committee tasked with investigating the airstrikes had in some cases denied that strikes had taken place despite "clear evidence" to the contrary, the report said.
In response to international concern over the strikes, Saudi officials have said that targeting practices are improving and that errant strikes are thoroughly investigated.
The report also found that the rule of law was "deteriorating rapidly across Yemen" as all parties to the conflict had carried out widespread violations of human rights. The panel had corroborated media reports that the United Arab Emirates — part of the Saudi-led military coalition — had tortured prisoners under its control. The Saudi-led coalition, which enforced a blockade on Yemen, was using the "threat of starvation as a bargaining tool and an instrument of war."
The Houthis had carried out extrajudicial executions and mass detentions, fueling a cycle of revenge that "may last for years."
The war, in the Arab world's poorest country, shows no end in sight, the panel wrote. "All parties to the conflict continue to believe that they can achieve a military victory that would negate the necessity for political compromise."
"Political decision makers on all sides are not bearing the brunt of the war," the report added. "Yemeni civilians are."