A U.S. drone strike on a recent wedding procession in Yemen — that left 12 people dead and at least 15 wounded — raises serious doubts about the Obama administration’s claim that so-called targeted killings do not harm civilians, charged Human Rights Watch in a report released Thursday.

Entitled , the 28-page report demands that the U.S. government investigate the incident and publicly account for any slaughter of civilians or violation of international law.

“The U.S. refusal to explain a deadly attack on a marriage procession raises critical questions about the administration’s compliance with its own targeted killing policy,” said Letta Tayler, senior terrorism and counterterrorism researcher at Human Rights Watch and author of the report. “All Yemenis, especially the families of the dead and wounded, deserve to know why this wedding procession became a funeral.”

The report decribes in harrowing detail the December 12th, 2013 launch of four hellfire missiles at a wedding procession near the city of Rad’a.

“Blood was everywhere, the bodies of the people who were killed and injured were scattered everywhere,” testified Abdullah Muhammad al-Tisi, a local sheikh, who was injured and lost his son Ali Abdullah, a 36-year-old father of three, in the attack. “I saw the missile hit the car that was just behind the car driven by my son. I went there to check on my son. I found him tossed to the side. I turned him over and he was dead. He was struck in his face, neck, and chest. My son, Ali!”