Last month, a CNN investigation found remnants of a US-made bomb at the scene of an airstrike that left dozens of schoolboys dead. Now, an independent Yemen-based human rights group called Mwatana has given CNN exclusive access to a trove of documents that show fragments of US-manufactured bombs at the scene of a string of other incidents since 2015, when the civil war began. In each of those cases, civilians were either killed or put at risk.

Mwatana, which documents violations by all parties in Yemen’s conflict, used its network of trained field researchers to photograph evidence at the scene of strikes. The group consulted weapons experts to identify the weapons used from serial numbers found on the fragments. Mwatana was recognized last month with an award by US body Human Rights First.

While CNN was not on the ground, we have made our own checks using image metadata and publicly available government websites linking each of these incidents to a US manufacturer. An internationally renowned weapons expert also analyzed each image for CNN.

The incidents give a snapshot of US involvement in Yemen’s conflict through its support for the Saudi-led coalition that is battling a Houthi-led rebel insurgency. The United States says 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.

Video: US-made weapons linked to Yemen deaths 5:25

Mwatana’s chairwoman, Radhya al-Mutawakel, told CNN that the US bore a “legal and moral responsibility for selling weapons to the Saudi-led coalition” that are worsening the conflict in Yemen.

“In more than one way and during more than one incident, remnants of American weapons have been found at the site of airstrikes that killed civilians,” she told CNN from Geneva, Switzerland. “Yemeni civilians are dying every day because of this war and you (America) are fueling this war, so stop fueling this war. It is a shame that financial interests are worth more than the blood of innocent people.”

Cdr. Rebecca Rebarich, a spokeswoman for the Pentagon, told CNN that “the final decisions on the conduct of operations in the campaign are made by the members of the Saudi-led coalition, not the United States.” Rebarich called “upon all parties to take all feasible precautions to avoid harm to civilians” and said the US took “all credible accounts of civilian casualties seriously.”