Multiple bomb fragments at the scene appear to confirm the use of American-produced MK-82 guided bombs. One fragment, posted in a picture on the Facebook page of a prominent Yemeni lawyer, says “FOR USE ON MK-82 FIN, GUIDED BOMB.”

Aircraft from the Saudi-led coalition on Saturday bombed a community hall in Sana’a, Yemen’s capital city, where thousands of people had gathered for a funeral for Sheikh Ali al-Rawishan, the father of the rebel-appointed interior minister. The aircraft struck the hall four times , killing more than 140 people and wounding 525. One local health official described the aftermath as “ a lake of blood .”

Fragments of what appear to be U.S.-made bombs have been found at the scene of one of the most horrific civilian massacres of Saudi Arabia’s 18-month air campaign in Yemen.

New evidence from the crime scene (Funeral hall) that was bombed by #Saudi fighters. MK82 guided bomb.The serial number will lead us. #Yemen pic.twitter.com/5Ch4WtF9tz

ITV News correspondent Neil Connery visited the site shortly after the attack, and found a similar bomb fragment . Connery said he was told by a Yemeni official that it appeared to be a MK-82 bomb.

#Video New evidence from the crime scene (Funeral hall) that was bombed by #Saudi fighters. MK82 guided bomb. #StopArmingSaudi #Yemen pic.twitter.com/iLw6PWO560

The MK-82 is a 500-pound explosive weapon manufactured in the United States. The code “96214” indicates that the bomb was produced by Raytheon, the third-largest defense contractor in the United States.

Saudi Arabia’s bombing campaign in Yemen began in March 2015 after Houthi rebels deposed the U.S.- and Saudi-backed dictator, Abd Rabbuh Mansur Hadi. Since the war began, Saudi Arabia has intentionally targeted numerous homes, factories, markets, schools, and hospitals.

The U.S. has supplied Saudi Arabia with more than $20 billion worth of weapons during its Yemen campaign, including thousands of MK-82 bombs. In November, the State Department approved the sale of 8,020 new MK-82 bombs as part of a $1.29 billion transfer of more air-to-ground weapons.

Throughout his presidency, President Obama has sold more than $115 billion worth of weapons to the Saudis – more than any other President. But after Saturday’s massacre, the Obama White House issued its first public threat to cut its support.

“U.S. security cooperation with Saudi Arabia is not a blank check,” Ned Price, spokesman for the White House National Security Council, said in a statement. Price added that the administration is “prepared to adjust our support so as to better align with U.S. principles, values and interests.”

On Monday, Reuters reported that Obama administration lawyers have not reached a conclusion on whether the U.S. is a “co-belligerent” in the conflict according to international law, a distinction that might raise legal risks and obligations. But since the U.S. has flown refueling missions for Saudi aircraft and supplied Saudi Arabia with weapons and targeting intelligence, it is complicit in Saudi Arabia’s atrocities by any normal definition.

As Bruce Riedel, a 30-year CIA officer and senior fellow at the Brookings Institute, said in April, “If the United States and the United Kingdom, tonight, told King Salman [of Saudi Arabia] ‘this war has to end,’ it would end tomorrow. The Royal Saudi Air Force cannot operate without American and British support.”