Saudi-led coalition air strikes have killed dozens of people in northern Yemen, including children travelling on a bus, Yemeni health officials and the International Committee of the Red Cross (ICRC) said.
The Western-backed alliance fighting the Iranian-aligned Houthi group in Yemen said in a statement that the air strikes targeted missile launchers used to attack the southern Saudi Arabia industrial city of Jizan, killing a Yemeni civilian there.
It accused the Houthis of using children as human shields.
Houthi spokesman Mohammed Abdul-Salam said the coalition showed "clear disregard for civilian life" as the attack had targeted a crowded public place in the city.
The ICRC said one attack hit the bus carrying children in Dahyan market, in northern Saada province, adding that hospitals there had received dozens of dead and wounded.
Abdul-Ghani Nayeb, head of a health department in Saada, said the death toll was to 43, with 61 wounded.
The Red Cross said that at least 29 children were killed.
Saudi Arabia and Sunni Muslim allies intervened in Yemen's war in 2015 against the Houthis, who control the most populous areas of Yemen, including the capital Sanaa, and drove the internationally recognised government into exile in 2014.
The United States and other Western powers provide arms and intelligence to the alliance, and human rights groups have criticised them over coalition air strikes that have killed hundreds of civilians at hospitals, schools and markets.
The alliance says it does not intentionally target civilians and has set up a committee to probe alleged mass casualty airstrikes, which has mostly cleared the coalition of any blame.
"Today's attack in Saada was a legitimate military operation ... and was carried out in accordance with international humanitarian law," the coalition said in the Arabic-language statement carried by SPA.
"Targeting Saudis and residents in Saudi is a red line," coalition spokesman Turki al-Malki later told Al Arabiya TV.
Fragments from the Houthi missile launched at Jizan Industrial City had killed one Yemeni civilian and wounded 11, Saudi state media said.
The Houthis have launched a series of missile strikes on the kingdom, including Riyadh, over the past year.
Saada, the main stronghold of the Houthis, has mainly come under air strikes from the coalition as the mountainous province makes battles hard for pro-government ground troops.
The Yemen war has killed more than 10,000 people, displaced more than two million and driven the country to the verge offamine, according to the United Nations.