But Kamel Jendoubi, who heads the so-called Group of Independent Eminent International and Regional Experts, insisted that "in light of the gravity of the situation and the limited time given to the mandate, additional investigations are needed."

The resolution that first set up the inquiry last year after a long diplomatic fight gave investigators a year to conduct their probe.

The investigators, appointed by the UN Human Rights Council a year ago, presented a report to the body that concluded all sides in Yemen's conflict may have committed "

War crimes investigators called Wednesday for the UN's top rights body to let them continue probing the "extremely alarming" situation in Yemen, amid resistance from Saudi Arabia and others.

"The situation in Yemen continues to be extremely alarming," he told the council.

"We call upon you to keep the situation in Yemen at the top of the priorities of the council," he said, urging diplomats to "unanimously" adopt a resolution led by a group of European countries and Canada calling for a one-year extension.

This, he said, was necessary "to ensure that truth is revealed and accountability is attained."

'Politicised and biased'

Three quarters of the population -- or 22 million people -- in need of humanitarian aid (photo by: ESSA AHMED/AFP)

But while a long line of diplomats voiced support Wednesday for prolonging the probe, it remains unclear if the council will give the investigators a green light to continue when it votes on the resolution at the end of this week.

A competing text on the table, led by Tunisia on behalf of the group of Arab states, makes no mention of extending the probe but calls for Yemen's often-criticised National Commission of Inquiry to continue studying the conflict.

Observers say Saudi Arabia, which leads a coalition that intervened in the conflict in March 2015 on behalf of President Abedrabbo Mansour Hadi's government in the fight against Iran-backed Huthi rebels, is actively working to quash the international probe.

Yemeni Human Rights Minister Mohamed Asker slammed the group's report as "politicised and biased".

He accused the investigators of ignoring "terrible crimes committed by the Huthis", who seized the capital Sanaa in 2014.

Saudi Arabia's ambassador to the UN, Abdulaziz Alwasil, charged that investigators h

ad based their findings on "conjectures and guesswork".

Human Rights Watch last week criticised Riyadh's "campaign to discredit and undermine a UN investigation into abuses by all Yemen’s warring parties," calling it "yet another blatant attempt to avoid scrutiny of the coalition's own actions in Yemen."

While investigators described violations by all sides, they concluded in their report that "coalition air strikes have caused most of the documented civilian casualties."

Yemen's conflict has left nearly 10,000 people dead since March 2015.

It has sparked the world's worst humanitarian crisis, with three quarters of the population -- or 22 million people -- in need of humanitarian aid, according to UN figures.