Washington, Aug 19 (IANS): A bomb used by the Saudi-led coalition in a devastating attack on a school bus in Yemen was sold as part of a US State Department-sanctioned arms deal with Saudi Arabia, munitions experts told CNN.

Working with local Yemeni journalists and munitions experts, CNN has established that the weapon that left dozens of children dead on August 9 was a 227 kg laser-guided MK 82 bomb made by Lockheed Martin, one of the top US defence contractors.

The bomb was very similar to the one that wreaked devastation in an attack on a funeral hall in Yemen in October 2016 in which 155 people were killed and hundreds more wounded.

The Saudi coalition blamed "incorrect information" for that strike, admitted it was a mistake and took responsibility.

In the aftermath of the funeral hall attack, former US President Barack Obama banned the sale of precision-guided military technology to Saudi Arabia over "human rights concerns".

The ban was overturned by the Trump administration's then Secretary of State Rex Tillerson in March 2017.

The August 9 bomb's impact as it landed on the bus full of excited schoolchildren on a day trip was devastating.

Of the 51 people who died in the airstrike, 40 were children.

The UN has called for a separate investigation into the strike, one of the deadliest since Yemen's war began in early 2015.