Credit: MOHAMMED HAMOUD/ANADOLU AGENCY/GETTY IMAGES Yemenis protest Saudi-led airstrikes during a rally on the first anniversary of the conflict.

WASHINGTON -- U.S.-supplied weapons were used by the Saudi Arabia-led coalition in one of its deadliest attacks in Yemen, Human Rights Watch, a nonprofit organization that surveyed the scene of the March 15 bombing, wrote in a report on Thursday.

Saudi Arabia and its Gulf allies have waged a bombing campaign in Yemen for over one year, with the stated goal of weakening the Houthi separatist group. But the coalition has faced criticism for indiscriminate bombings that have hit civilian targets, including hospitals, schools, weddings and markets. One hundred and seven people, including 25 children, were killed in the dual airstrikes on a market in northwestern Yemen last month, said Human Rights Watch. The United Nations identified and named 97 of the victims as civilians, but another 10 bodies were charred beyond recognition by the blasts.

A witness told Human Rights Watch he recognized the bodies of about 10 Houthi fighters who were killed in the blasts and said that Houthi fighters often ate and slept at a nearby restaurant. The group could not corroborate his claims. Brig. Gen. Ahmed al-Assiri, a spokesman for the Saudi-led military coalition, told AFP last month that the target of the strike was a “militia gathering,”

After investigating the site of the blast on March 28, the human rights group found the remains of a “GBU-31 satellite-guided bomb, which consists of a US-supplied MK-84 2,000-pound bomb mated with a JDAM satellite guidance kit, also US-supplied.” The New York Times reported that U.S. warplanes typically use smaller bombs, closer to 500 pounds, in order to reduce the risk of killing civilians.

The JDAM kit, or Joint Direct Attack Munition, is a U.S. technology that converts unguided bombs into “smart” munitions.

The U.S. justifies its backing of Saudi Arabia and its partners in its air war over Yemen by claiming that American assistance helps the coalition strike with more precision, minimizing civilian casualties. When asked if the high civilian death toll in the March 15 attacks challenged this narrative, the Pentagon remained on-message.

“The U.S. is confident that the information that we relay and non-combat support we provide to Saudi Arabia and other Coalition members is sound and provides them the best options for military success consistent with international norms and specifically mitigating the potential for civilian casualties,” Col. Patrick Ryder, a U.S. Central Command spokesman, said.

The Pentagon has said in the past that it provides “targeting assistance” to the Saudi-led coalition, but Ryder emphasized on Thursday that the U.S. does not have a final say in selecting and vetting targets.

A senior administration official pointed to Saudi’s announcement that it would form a commission to investigate incidents of civilian casualties as a “vital step” and called on “all parties in Yemen” to “comply with the laws of war." (The Houthi separatists have also been accused of launching indiscriminate attacks that cause civilian casualties.)

Groups like Human Rights Watch and Amnesty International, another human rights nonprofit, are dismissive of the Saudi pledge to self-investigate and have instead called for an independent investigation into possible war crimes.

Saudi Arabia began bombing Yemen last March at the request of Yemeni President Abd-Rabbu Mansour Hadi, who had been forced out of the capital by the Houthis. The Houthis receive weapons and support from Iran, but the Iranians do not exert direct control over the group.

Over 6,000 people have died in the yearlong conflict in Yemen, with half estimated to be civilians. A U.N.-brokered ceasefire is set to go into effect April 10, followed by a new round of peace talks.

The U.S. decision to back the Saudi-led operation in Yemen is thought to be threefold:

Saudi Arabia is a key U.S. ally.

The U.S. has an interest in limiting Iranian influence in the Middle East.

The Saudi air war began as the U.S. and its international partners were working to complete a nuclear agreement with Iran, Saudi Arabia’s rival in the region. Lending support to Riyadh was likely part of an effort by Washington to reassure its ally of the continuing strength of their relationship.

But at least one lawmaker has challenged that rationale and called for the U.S. to suspend military sales to Saudi Arabia and its support of the Saudi-led war in Yemen until Congress receives assurances the coalition's actions aren't fueling instability in Yemen, which could in turn strengthen groups like al Qaeda and the Islamic State.

“With little public debate, the U.S. has a key role in a misguided war that has killed 3,000 innocent civilians. While all sides clearly share responsibility for the violence, the UN reported that most civilian deaths are the result of the Saudi-led coalition’s aerial bombing,” said Chris Murphy (D-Conn.), a member of the Senate Foreign Relations Committee, after the attack.

“The U.S. has no business getting involved in a war that has only served to empower our terrorist enemies, exacerbate a humanitarian crisis, and incite fear and anger among the Yemeni people toward the United States,” Murphy added.