BERLIN (AP) — The head of the United Nations human rights office called Saturday for a prompt, transparent investigation into the deaths of at least 28 people whose bodies were found in northwest Burkina Faso last month.

Volker Türk, the U.N. High Commissioner for Human Rights, said it was encouraging that authorities had announced an investigation into the incident in Nouna town, a predominately ethnic Fulani and Muslim community.

"I call on them to ensure it is prompt, thorough, impartial and transparent and to hold all those responsible to account regardless of position or rank,” he said in a statement.

“The victims and their loved ones are owed no less,” he added.

Local human rights groups allege that volunteer militias supporting Burkina Faso's army killed dozens of Fulani civilians, including children. Fulani people have been increasingly targeted by the military and local defense militias because they are suspected of supporting the West African country's Islamic extremist rebels who have been inflicting violence on the country for years.

The U.N. human rights office said Türk had previously raised concerns with the government about possible abuses “linked to recruitment, arming and deployment of auxiliaries in Burkina Faso.”

“There is an urgent need to strengthen their vetting procedures, predeployment training on international human rights and humanitarian law, their effective supervision by the security and defence forces and to ensure inclusion and transparency during their recruitment,” the Geneva-based office said.