Munitions experts have told US news network CNN the bomb used by the Saudi-led coalition was sold as part of a US State Department-sanctioned arms deal with Saudi Arabia.
Dozens of children were killed on August 9 during an attack on a bus at a market in rebel-held northern Yemen.
The incident sparked global outrage, with the US joining UN calls for an investigation into the strike.
CNN said it has been working with Yemeni journalists and munitions experts and have established that the weapon was a 227 kilogram laser-guided MK 82 bomb made by Lockheed Martin, one of the top US defense contractors.
It is also reporting that the bomb is "very similar" to the one used in an attack on a funeral hall in Yemen 2016, which killed 155 people and left hundreds wounded.
Amid the investigation into the attack, questions over whether the US was complicit are mounting.
According to CNN, the White House said it "does not make targeting decisions for the coalition but it does support its operations through billions of dollars in arms sales, the refueling of Saudi combat aircraft and some sharing of intelligence."
