Weapons provided by Western powers and Iran to the warring sides in Yemen are fuelling the six-year-old conflict, marked by deadly Saudi-led coalition air strikes and Houthi shelling, U.N. investigators said on Wednesday.

Coalition air strikes in the past year may amount to war crimes, while the Iran-aligned Houthi movement carried out killings and other abuses that may also constitute war crimes, they said.

It was the third successive year that the panel of independent experts found that all parties had violated international law. This year's findings covered incidents from June 2019 to June 2020.

Countries including Britain, Canada, France, Iran and the United States continued their support to the warring sides "including through arms transfers, thereby helping to perpetuate the conflict", the U.N. panel said in a report entitled "Yemen: A Pandemic of Impunity in a Tortured Land".

"After years of documenting the terrible toll of this war, no one can say 'we did not know what was happening in Yemen'," said Kamel Jendoubi, chairman of the Group of Experts.

The three experts urged the U.N. Security Council to refer the situation in Yemen to the International Criminal Court (ICC) for possible prosecutions.

The Saudi-led Sunni Muslim coalition intervened in Yemen in March 2015 after the Houthis ousted the internationally recognized government from power in the capital, Sanaa, in 2014.

The conflict is widely seen as a proxy war between Saudi Arabia and its regional foe, Shi'ite Muslim Iran. More than 100,000 people have been killed and millions are on the brink of famine, aid agencies say.

"During this reporting period, the Group verified a further four airstrikes or series of airstrikes involving similar failures to take all necessary measures to protect civilians and civilian objects," the report said of the coalition backing the government of Yemen's exiled president, Abd-Rabbu Mansour Hadi.

"Disproportionate attacks constitute war crimes under customary international law," it said.

They included "one of the deadliest airstrikes of 2020", launched by the coalition on Feb. 15 on a village in the Al-Hayjah area of Al-Jawf province, "resulting in approximately 50 civilians killed and injured," it said.

"The coalition's restrictions on imports and access to Al-Hudaydah (Hodeidah) port have contributed to shortages of fuel and other necessities and to inflation, thereby exacerbating the economic and humanitarian crisis," the U.N. panel said.

Mortar bombs fired by the Houthis hit a central prison in the frontline city of Taiz in April, killing six women and two girls, according to the report, which said it could constitute a war crime.