"The United States' ability to help Mali on the security side is greatly constrained now... by the choice that the Mali government made to get into bed with Wagner," Victoria Nuland, the US State Department's under secretary for political affairs, told reporters following a four-day visit to the Sahel.
"Terrorism [in Mali] has gotten significantly worse," Nuland said, claiming that such incidents rose some 30 percent over the past six months.
Nuland said there were "broad reports of human rights abuses across the region where (Wagner forces) are working" and accused the operatives of giving "malfunctioning" equipment to Mali's army and encouraging it to deny the UN peacekeeping mission access to "large swathes" of the country.
The mission, MINUSMA, has itself complained that the junta is limiting its operations.
Nuland said the Russian-owned mercenaries' presence had also constrained U.S. operations in the West African country.
"We are just not going to operate in the same space, even if we were invited to or able to, because of the negative way (Wagner forces) operate, the way they treat people", she said. "We are limited by the bad security choices that the junta has made."
French forces, which had been operating for about a decade in Mali, completely withdrew earlier this year.
The United States had provided logistical and intelligence support to France's Barkhane force before it relocated to Niger. Nuland said the American army's Africa Command has continued to work very closely with that force despite its redeployment.
She said Mali's neighboring countries are "extremely concerned" and want to "ensure that Wagner and terrorism both stay on the Malian side of the border."
Nuland, who said she met with Mali's interim prime minister and government, said the junta appeared to remain committed to its promise to hold elections in 2024.
Along with Mali, the State Department official's tour included a stop in Burkina Faso, where she heard from interim president, Ibrahim Traore, who seized power in a coup last month, that the country would not turn to Russian operatives for support in fighting jihadists.
"He was unequivocal in saying that it is Burkinabe who will defend the security of their nation and that they have no intention of inviting Wagner in", she said.
Nuland also visited Niger and Mauritania, referring to the latter as an "island of stability in a very, very rough neighborhood."