The Saudi-led coalition on Saturday said "mistakes" had been made in the August 9 strike on a crowded marketplace in a part of northern Yemen held by Huthi rebels that the Red Cross said had killed 51 people.

The incident sparked a wave of international anger and calls by the United Nations Security Council for a "credible and transparent" investigation.

"We welcome the speed of the investigation into the incident of 9 August, and the coalition's announcement of regret and action to address the recommendations of that investigation," said the British Foreign Office.

"We are reviewing the investigation's conclusions," it added.

The coalition had claimed to have targeted a bus carrying rebels.

Separately on Sunday, the US State Department called the Saudi-led coalition's investigation into the August 9 attack "an important first step toward full transparency and accountability".

Britain, however, asked the coalition to provide information on two other deadly incidents.

It welcomed the opening of a separate investigation into air strikes on August 23 south of the rebel-held port city of Hodeida that killed 26 children and four women.

"(We) encourage the publication of the outcomes of this investigation as soon as possible," it said.

It also urged "clarification of the circumstances around the incident of 2 August", when explosions in the rebel-held port city of Hodeida killed at least 55 people.

Britain had "serious concern at the tragic loss of life in Yemen over the last month," violence it said killed 400 Yemenis in the first two weeks of August alone.

UN investigators said Tuesday that all sides in Yemen's conflict may have committed war crimes, highlighting deadly air strikes, rampant sexual violence and the recruitment of young children as soldiers.

The Saudi-led coalition intervened in Yemen in March 2015 after the Huthis ousted President Abedrabbo Mansour Hadi's government from the capital Sanaa and seized swathes of the country.

The devastating conflict has since left nearly 10,000 people dead and sparked what the UN has described as the world's worst humanitarian crisis.