Saudi Arabia announced an easing of its 18-month air blockade of rebel-held areas of neighbouring Yemen on Wednesday to allow the evacuation of hundreds of wounded from a deadly weekend air strike.

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 Huthi Shiite 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.

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.

The coalition has enforced an air and sea blockade on rebel areas since the start of its bombing campaign, with exceptions made only for UN flights and UN-supervised aid deliveries, most of them through the Red Sea port of Hodeida.

The rebel-controlled civil aviation authority in the Yemeni capital had called on the United Nations on Tuesday to "act quickly and seriously to end the air blockade imposed on Sanaa airport in order to save the lives of hundreds wounded."

The coalition initially denied responsibility for Saturday's air strike but after condemnation from Western governments, it promised an investigation of the "regrettable and painful" incident.

A letter sent to the UN Security Council on Sunday "expressed the kingdom's deep regret" over the "attack", state media reported the following day.

"It also renewed its full respect for and commitment to international humanitarian law and international human rights law, and the emphasis on continuing to ensure the taking of all possible measures to protect civilians and civilian sites in Yemen".

The coalition has faced mounting international criticism over the civilian casualties from its bombing campaign.

Washington has also come under increasing pressure over the intelligence and logistics support it has provided.

More than 6,800 people have been killed in Yemen since the coalition started its campaign.

More than two-thirds of them have been civilians, most of them killed in coalition air strikes.