The African Union has admitted that its soldiers in Somalia were responsible for the killing of seven civilians at a wedding last month, Agence France-Presse reported. The organization had previously denied the allegations, but issued an apology Friday following a Human Rights Watch report that found evidence of the massacre and called on the Africa Union to launch its own investigation.

Witnesses in the Somali port town of Marka told news outlets immediately following the July 21 killings that AU troops opened fire on civilians after a militant from the al Qaeda-affiliated al-Shabab group lobbed a grenade at a passing AU convoy. Initial reports indicated that at least two-dozen civilians were gunned down. 

Hours later, the African Union Mission in Somalia, or Amisom, denounced the “devious allegations” being made against its soldiers as untrue. However, Human Rights Watch, a rights group based in New York City, found evidence supporting charges that at least six men were massacred in “cold blood” at a wedding following the al-Shabab attack.

"At one house, where the Moalim Iidey family was celebrating a wedding, the soldiers separated the men from the women and shot the six adult men -- four brothers, their father, and an uncle," the Human Rights Watch report said.

Amisom leader Maman Sidokou apologized for the killings Friday, acknowledging that seven civilians were killed.

"I would like on behalf of the African Union, to offer my sincere apology for these deaths. We regret these deaths," he said in a statement. "I have instituted a board of inquiry composed of military, civilian and police officers who are not from the contingent concerned in order to ensure impartiality."

The statement added that three Amisom personnel, all of them Ugandan soldiers, have been indicted and are awaiting a military judicial process.

Amisom and the military have been fighting an eight-year insurgency by the al-Shabab militant group. The insurgents have launched a campaign to drive out the Somali government from large swaths of the country and impose their own narrow interpretation of Islamic law. They have been responsible for thousands of civilian and soldier deaths.

Al-Shabab has lost some of its key territory in recent months as the Somali government and African Union have stepped up a campaign meant to destroy the group.