Rights group calls Saudi-led coalition bombing an apparent war crime that places ‘arms suppliers at risk of complicity’.

The Human Rights Watch (HRW) has called for an end to all weapons sales to Saudi Arabia following the bombing of a school bus last month that killed 51 people, including 40 children.

The rights group called the attack an apparent war crime and said it places arms suppliers at “risk of complicity in war crimes”.

HRW’s statement, released on Sunday, came just hours after Saudi Arabia and the United Arab Emirates admitted the bombing was “unjustified”.

A probe, conducted by the Saudi-led coalition fighting Yemen’s Houthi rebels, concluded on Saturday that “mistakes” were made in the August 9 air raid in Saada province.

The coalition, which initially defended the bombing saying it hit a “legitimate military target”, has now pledged to hold to account those responsible for the attack.

HRW said it received photographs and videos of munition fragments that a lawyer based in Sanaa, about 235km south of Saada, said were at the site.

Markings visible on photos and videos of one of the remnants – a guidance fin for a GBU-12 Paveway II bomb, an aerial laser-guided bomb – show it was produced by Pentagon’s top weapons supplier Lockheed Martin, according to the rights group.

HRW also said that while it could not confirm the remnants were found at the site of the attack, images of damage from the scene are consistent with the detonation of a large, impact-fused aerial bomb.

Al Jazeera could not reach Lockheed Martin for a comment.

“The Saudi-led coalition’s attack on a bus full of young boys adds to its already gruesome track record of killing civilians at weddings, funerals, hospitals, and schools in Yemen,” said Bill Van Esveld, senior children’s rights researcher at HRW.

“Countries with knowledge of this record that are supplying more bombs to the Saudis will be complicit in future deadly attacks on civilians.”

Saudi Arabia, along with the UAE, has been bombing Yemen since March 2015 after the Houthis swept across the country. The coalition’s stated aim is to restore the government of President Abd-Rabbu Mansour Hadi to power.

Out of the 16,000-plus raids they have launched since the start of the conflict, only a handful have been investigated, despite nearly a third of all bombs hitting civilian targets.

Al Jazeera’s Alan Fisher, reporting from neighbouring Djibouti, said the report added to mounting pressure on the US to end its support for the Saudi-led coalition.

“In the US, there’s a growing movement urging the government to pull back support for the coalition, particularly when rights groups are saying that if the Saudis commit a war crime, and they use a US weapon, then the US could be complicit in that,” he said.

The international outcry over the Saada attack also put pressure on the warring sides in Yemen to reach an agreement when they meet for UN-sponsored peace talks in Geneva later this month, Fisher added.

HRW said it has identified US-origin munitions at the sites of at least 24 other coalition attacks in Yemen.

In November 2015, the US approved the sale of 4,020 GBU-12 Paveway II bombs as part of a $1.3bn arms sale to Saudi Arabia, but halted parts of the sale in December 2016.

President Donald Trump’s administration, however, has reversed that decision.

The UK and France remain major arms sellers to Saudi Arabia, HRW said. Germany and Norway have suspended arms sales to the Kingdom, while the Netherlands and Sweden have limited weapons sales.

Last year, the UN blacklisted the Saudi-UAE alliance for causing the majority of reported child deaths and injuries in Yemen. It also described the situation in Yemen as the world’s worst humanitarian crisis.

At least 10,000 people have been killed since the start of the conflict, the UN said.