The bomb used by the Saudi-led coalition in a devastating attack on a school bus in Yemen was sold as part of a U.S. 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 500-pound (227 kilogram) laser-guided MK 82 bomb made by Lockheed Martin, one of the top U.S. defense contractors.

The bomb is 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 March of that year, a strike on a Yemeni market -- this time reportedly by a U.S.-supplied precision-guided MK 84 bomb -- killed 97 people.

In the aftermath of the funeral hall attack, former U.S. 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.

As the U.S.-backed Saudi-led coalition scrambles to investigate the strike on the school bus, questions are growing from observers and rights groups about whether the U.S. bears any moral culpability. The U.S. says it does not make targeting decisions for the coalition, which is fighting a Houthi rebel insurgency in Yemen. But it does support its operations through billions of dollars in arms sales, the refueling of Saudi combat aircraft and some sharing of intelligence.

"I will tell you that we do help them plan what we call, kind of targeting," said U.S. Secretary of Defense James Mattis. "We do not do dynamic targeting for them."

The latest strike has left the community in Yemen's northern Saada governorate reeling.

Zeid Al Homran visits the graveyard where his two little boys are buried every day. On this occasion, he brought their five-year-old brother along. He is all Al Homran has left.

"I was screaming in anger and all around me women were throwing themselves on the ground," he told CNN. "People were screaming out the names of their children. I tried to tell the women it couldn't be true but then a man ran through the crowd shouting that a plane had struck the children's bus."