GENEVA (AP) — Independent human rights experts working with the U.N. on Tuesday called for an investigation of possible abuses, war crimes and crimes against humanity committed by government forces in Mali and the Wagner Group, a shadowy Russian military contractor.

More than a dozen experts, who focus on issues as various as the use of mercenaries, torture, and violence against women and girls, cited accounts of “horrific executions, mass graves, acts of torture, rape and sexual violence” and other alleged crimes over the last two years by government forces and “their allies” in the area of central Mopti and elsewhere in the restive West African country.

“We are particularly worried by credible reports that over the course of several days in late March 2022, Malian armed forces accompanied by military personnel believed to belong to the Wagner Group, executed several hundred people, who had been rounded up in Moura, a village in central Mali,” the experts said in a statement.

The experts said they were “disturbed by the apparent increased outsourcing of traditional military functions to the so-called Wagner Group in various military operations.”

Western officials say hundreds of fighters from the Wagner Group began working more than a year ago alongside Mali’s armed forces to try to stem a decade-long insurgency by Islamic extremists in the West African country.

Diplomats, analysts and human rights groups say indiscriminate violence against civilians has grown since the mercenaries arrived, warning that extremists linked to al-Qaida and the Islamic State group have only become stronger.

The outside experts, who aren’t U.N. staff, work under a mandate from the U.N.-backed Human Rights Council in Geneva to help keep tabs on a vast array of human rights concerns around the world.

“The lack of transparency and ambiguity over the legal status of the Wagner Group, combined with reprisals against those daring to speak out, create an overall climate of terror and complete impunity for victims of the Wagner Group’s abuses,” the experts said, adding that they’ve relayed their concerns directly to the government in Bamako.