As funeral ceremonies for the 51 Yemenis—including 40 young children—massacred by the latest U.S.-backed Saudi bombing took place in the war-torn district of Saada on Monday, cellphone footage captured by one of the murdered children just moments before the coalition’s airstrike hit shows the dozens of kids excitedly gathered on a bus for a long-awaited field trip celebrating their graduation from summer school.

“By backing the Saudi coalition’s war in Yemen with weapons, aerial refueling, and targeting assistance, the United States is complicit in the atrocities taking place there.”
—Sen. Bernie Sanders

According to CNN—which obtained and published the footage on Monday—most of the children on the bus were killed by the Saudi airstrike less than an hour after the video was captured.

This is just the latest horrific attack on civilians by the Saudi-led coalition, which has received explicit military and political backing from the United States. Images sent to Al-Jazeera by Yemen’s Houthi rebels suggest that Mark-82 bomb—which is manufactured by the massive American military contractor Raytheon—was used in the strike, though the photos have yet to be independently verified.

Watch the footage (warning, the video is graphic):

According to the Houthi Health Ministry, 79 people in total and 56 children were wounded in the attack, which quickly drew condemnation and demands for an independent investigation from international humanitarian groups, the United Nations, and a small number of American lawmakers.

“By backing the Saudi coalition’s war in Yemen with weapons, aerial refueling, and targeting assistance, the United States is complicit in the atrocities taking place there,” Sen. Bernie Sanders (I-Vt.) wrote on Facebook. “We must end our support for this war and focus our efforts on a U.N.-brokered cease-fire and a diplomatic resolution.”

As Al-Jazeera notes, the U.S. “has been the biggest supplier of military equipment to Riyadh, with more than $90 billion of sales recorded between 2010 and 2015.”