According to CNN.COM ,The 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,
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.As the US-backed Saudi-led coalition scrambles to investigate the strike on the school bus, questions are growing from observers and rights groups about whether the US bears any moral culpability.
Source : CNN.COM
The US 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.
For more informations : https://edition.cnn.com/2018/08/17/middleeast/us-saudi-yemen-bus-strike-intl/index.html