WASHINGTON (AP) — A U.S. military drone strike in Yemen last December may have killed up to a dozen civilians on their way to a wedding and injured others, including the bride, a human rights group says. U.S. officials say only members of al-Qaida were killed, but they have refused to make public the details of two U.S. investigations into the incident.

Human Rights Watch released a report on the drone strike Thursday, citing interviews with eight witnesses and relatives of the dead as well as Yemeni officials. The report said four Hellfire missiles were fired at a wedding procession of 11 vehicles on Dec. 12, 2013, in Radda in southern Yemen, killing at least 12 men and wounding at least 15 others, six of them seriously.