Britain has expressed "deep concern" over an airstrike that hit a bus carrying children in Yemen.

At least 50 people were killed in the attack on a market in Saada on Thursday, according to the Houthi-controlled health department.

The attack has been blamed on the Saudi-led coalition fighting Yemen's Houthi rebels.

Foreign Office minister Alistair Burt tweeted: "Deeply concerned by reports of yesterday's attack in Sa'ada, Yemen resulting in tragic deaths of so many children.

"Transparent investigation required. UK calls on all parties to prevent civilian casualties and to cooperate with UN to reach a lasting political solution in Yemen."


Image: It has been difficult to establish the number of people injured

As the UN chief Antonio Guterres called for a prompt independent investigation into the airstrike, UNICEF executive director Henrietta Fore issued a powerful statement condemning the attack.

She said: "The horrific attack on a bus in Saada, Yemen, reportedly killing and maiming scores of children, marks a low point in the country's brutal war.

"The question now is whether it will also be a turning point - the moment that must finally push the warring parties, UN Security Council and international community to do what's right for children and bring an end to this conflict."

Meritxell Relano, UNICEF's representative in Yemen, told Sky News: "This is the worst single attack ever on children since the conflict in Yemen escalated in 2015. Despite our repeated calls for respect of international humanitarian law, parties to the conflict in Yemen have acted with utter disregard.

Crying children treated after bus airstrike

"It is heartbreaking to see such innocent children attacked in this way."

Chaos on the scene means confirming the number of dead and injured at this early stage has been difficult.

According to rebel-run Al Masirah TV, the health ministry said the number of dead had risen to at least 50 and that 77 had been wounded in the strike.

The Red Cross said its team received the bodies of 29 children, all under 15 years old. They say they treated 48 wounded, 30 of them children.

UNICEF teams, who helped provide medical supplies, has so far only verified 21 children killed and 35 injured. Verification is still ongoing and the charity says the figure could rise.

Image: The airstrike struck a bus carrying children

Ms Fore warned that the conflict's repeated attacks and access restrictions are hampering UNICEF's ability to reach those most in need, including 11 million children who require humanitarian assistance.

A UNICEF-supported water station and sanitation centre in Hodeida which provide families with access to clean water and help prevent another outbreak of cholera were attacked and seriously damaged in recent weeks.

"Parties to the conflict and those who have influence over them, including Security Council members, can and should choose to end this catastrophe for the sake of Yemen's children," Mrs Fore said.

Yemen's Houthi rebels welcomed the UN call for probe into Thursday's airstrike, as the Western-backed alliance accused the Iranian-backed Houthis of using children as human shields.

Image: The conflict has been described as a 'low point' in Yemen's war

The alliance said the strikes had targeted missile launchers used to attack the Saudi city Jizan on Wednesday, killing a Yemeni civilian there.

They say the attack was carried out in accordance with international humanitarian law.

Saudi Arabia and allies have been fighting in Yemen for more than three years against the Iran-backed Houthis, who control much of northern Yemen including the capital Sanaa and drove a Saudi-backed government into exile in 2014.

The UK and US have been criticised for providing logistical and military support to the Saudi-led coalition.

Yemen has become the world's worst humanitarian crisis, with more than 22.2 million people in need of assistance.