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Saudi Arabia said it would ease its 18-month air blockade of rebel-held areas of neighbouring Yemen on Wednesday to allow the evacuation of hundreds of wounded affected Saturday's deadly weekend air strike.

King Salman instructed aid officials to coordinate with the coalition and the Saudi-backed Yemeni government "to facilitate the evacuation of those wounded... and needing treatment abroad", the official Saudi Press Agency reported.

More than 140 people were killed in Saturday's raid on the wake for the father of a rebel leader in the Yemeni capital Sanaa that drew worldwide condemnation, including from key Riyadh ally Washington.

At least 525 more were wounded, according to the United Nations, making it one of the bloodiest attacks since a Saudi-led coalition launched a bombing campaign against the Houthi rebels in March 2015. 

More than 300 are in critical condition and need medical treatment abroad, the spokesman for the rebel-run health authority in Sanaa, Tamim al-Shami said on Sunday.

Among the victims are dozens of military officials, including the Mayor of Sanaa, Abdulqader al-Hilal.

On Monday, the UN called for swift action to bring to justice the perpetrators of airstrikes on a funeral ceremony in the Yemeni capital that killed more than 140 people.

"We must do everything possible to ensure the authors of these heinous attacks face justice," UN envoy Ismail Ould Cheikh Ahmed said in Paris after talks with French Foreign Minister Jean-Marc Ayrault.

The envoy said the Saudi-led coalition must publish the results of its probe into the strikes, which also injured more than 525 people.

"We need to have the results of the investigation under way very quickly," he said.

UN Secretary-General Ban Ki-moon said the airstrikes on a funeral ceremony was a "heartless attack on civilians and an outrageous violation of international humanitarian law".

He said an independent body to probe rights violations in Yemen must be set up.

"There must be accountability for the appalling conduct of this entire war," Ban told reporters.

The attack was among the deadliest in Yemen since the Riyadh-led alliance launched its aerial campaign against the rebels last year.

The coalition, which initially denied any involvement, said on Sunday it would investigate the incident, after the US said it was reviewing support for the alliance.

"The coalition will immediately investigate this case along with... experts from the United States who participated in previous investigations," it said.

The alliance was already under intense international scrutiny over the civilian death toll in its Yemen operations.