DAHYAN, Yemen (Dispatches) -- The remains of victims and children's clothing were strewn across a market in northern Yemen on Friday, as the UN called for an investigation into a Saudi airstrike the previous day that killed at least 50 people, including 30 children, on a bus.
Yemen’s Al-Masirah TV, quoting the Health Ministry, reported that 77 others were wounded, "mostly children,” when the bus traveling through a market was targeted in Yemen’s Saada province.   
Wounded children, bloodied, bandaged and screaming, laid on stretchers as doctors treated them, friends and relatives having carried them in their arms to be treated.
An AFP photographer at the scene said the bus carrying the children had been turned into a mass of twisted metal, and that the remains of victims and their personal data-x-items were scattered across the ground.
"There are remains everywhere, we are still trying to confirm identities," Yahya Shayem, a health official in Saada, told AFP.
The International Committee of the Red Cross said on Twitter that its team at an ICRC-supported hospital in Saada received the bodies of 30 children, all under 15 years old. It also received 48 wounded people, including 30 children, it said.
A spokesman for the Red Cross in Sanaa told AFP the toll was not final as casualties from the attack were taken to several hospitals.
UN Secretary-General Antonio Guterres urged an "independent and prompt" probe.
The attack took place in the Dahyan market in Saada province, a Houthi stronghold. The province lies along the border with Saudi Arabia.
The bus was ferrying local civilians, including many children coming from summer school, according to the Saada health department and Yemeni tribal leaders who spoke on condition of anonymity.
"Our shops were open and shoppers were walking around as usual. All of those who died were residents, children and shop owners,” witness Moussa Abdullah, who was being treated in hospital for wounds, told Reuters.
"We need blood," said Jameel al-Fareh, an emergency room doctor at Saada's Al-Jumhuri hospital, calling on local people to donate blood to treat the wounded.
Ahmed al-Mansouri, the hospital's director, condemned what he called the "massacre of children."
Saudi Arabia has been waging a destructive war on Yemen since March 2015 in a bid to reinstate a former president who resigned and then fled to Riyadh.
Yemenis fighting the Saudi invasion, including Houthis and their allies in the army, control much of northern Yemen, including the capital, Sanaa.
Col. Turki al-Malki, a spokesman for the Saudi military, said the attack in Saada came after Yemeni fighters fired a missile at the kingdom’s south, killing one person and wounding 11 others.
Malki insisted Thursday’s attack carried out in Saada was a "legitimate military action” and "in accordance with international humanitarian law and customs.”  He accused the Houthis of recruiting children and using them in the battlefields.
Last week, Saudi attacks on a hospital and a fish market in the strategic port city of Hudaydah killed at least 55 civilians and wounded 170, according to the ICRC.  
Aid agency CARE International noted that Thursday's strike came a week after the Hudaydah bombardment.
"This latest airstrike, only a week after the attacks on Hudaydah city, demonstrates a continued disregard for human life and suffering," said Johan Mooij, the agency's country director in Yemen. "It is beyond cruel; innocent children's lives have been lost."
The fight for the port of Hudaydah, a key lifeline for supplies and aid for Yemen’s population on the brink of starvation, has become the latest battleground in the devastating Saudi war.
The United Nations envoy to Yemen Martin Griffiths told the UN Security Council last week that "a political solution” to end the war in Yemen was "available” and that the warring sides would be invited to talks on Sept. 6 in Geneva.
The Saudi war in impoverished Yemen has left nearly 15,000 people dead and unleashed what the UN describes as the world's worst humanitarian crisis.