By Michelle Nichols

UNITED NATIONS, Jan 8 (Reuters) - Yemen's Houthi group did not launch an attack on Saudi Arabia's oil facilities in September, according to a confidential report by U.N. sanctions monitors seen by Reuters on Wednesday, bolstering a U.S. accusation that Iran was responsible.

The United States, European powers and Saudi Arabia blamed Iran for the Sept. 14 attack on the Saudi Aramco oil plants in Abqaiq and Khurais, dismissing a quick claim of responsibility by the Iran-allied Houthis. Tehran denied any involvement.

The report by the independent U.N. experts to the Security Council Yemen sanctions committee said, "That despite their claims to the contrary, the Houthi forces did not launch the attacks on Abqaiq and Khurais on 14 September 2019."

The findings of the U.N. report come amid escalating tensions in the region after the United States killed Iranian General Qassem Soleimani in Baghdad and Tehran retaliated by firing missiles at military facilities housing U.S. troops in Iraq.

The U.N. investigators said they doubted that the drones and land attack cruise missiles used in the Sept. 14 attack "have a sufficient range to have been launched from Yemeni territory under the control of the Houthis."

"The panel notes that Abqaiq and Khurais were approached respectively from a north/northwestern and north/northeastern direction, rather than from the south, as one would expect in the case of a launch from Yemeni territory," the report said.

The investigators, who monitor sanctions on Yemen, also said they do not believe that "those comparatively sophisticated weapons were developed and manufactured in Yemen." They were not tasked with identifying who was responsible for the Saudi attack.

MILITARY SUPPORT OF THE HOUTHIS

The attacks that targeted the Abqaiq and the Khurais oil plants caused a spike in oil prices, fires and damage, and shut down more than 5% of global oil supply. Saudi Arabia said on Oct. 3 that it had fully restored oil output.

The Saudi minister of state for foreign affairs, Adel al-Jubeir, signaled in September that Riyadh was waiting for results of U.N. investigations before announcing how his country would respond.

"The United Nations sent people to be part of the investigation, other countries have sent experts to be part of the investigation," he told reporters in New York. "When the team that's investigating has concluded its investigations we will make the announcements publicly."

Reuters reported in November that Iran's Supreme Leader Ayatollah Ali Khamenei had approved the attack on the Saudi oil facilities, but with strict conditions: Iranian forces had to avoid hitting any civilians or Americans. Iran rejected the version of events that four people described to Reuters.

U.N. experts monitoring U.N. sanctions on Iran and Yemen traveled to Saudi Arabia days after the September attack.

U.N. Secretary-General Antonio Guterres told the Security Council in a separate report on Dec. 10 - on the implementation of an arms embargo and other restrictions on Iran - that the United Nations was "unable to independently corroborate" that missiles and drones used in the attacks "are of Iranian origin."

The report seen by Reuters on Wednesday is from the independent panel of experts that reports twice a year to the Security Council on the implementation of sanctions related to the conflict in Yemen that were imposed in 2014 and 2015.

It was submitted to the U.N. Security Council Yemen sanctions committee on Dec. 27, but will not be made public until later this month or next month.

A proxy war has been playing out in Yemen between Iran and Saudi Arabia. The Saudi-led coalition intervened in 2015, backing government forces fighting the Iran-allied Houthis. The Houthis have been subject to a separate arms embargo since 2015. Iran has repeatedly denied supplying weapons to the Houthis.

"The Houthi forces continue to receive military support in the form of assault rifles, rocket propelled grenade launchers, anti tank guided missiles, as well as more sophisticated cruise missile systems," the report found.

"Some of those weapons have technical characteristics similar to arms manufactured in Iran," it said. (Reporting by Michelle Nichols Editing by Mary Milliken and Leslie Adler)

Our Standards: The Thomson Reuters Trust Principles.