Russian's Wagner group could be secretly trying to obtain military equipment for the war in Ukraine through its operations in Mali and other African countries, the US says.
A Treasury Department statement said the private military group's employees may be attempting to procure mines, drones and radar equipment.
Wagner is known to be operating in some African countries including Mali.
The statement also announced sanctions on Wagner's Mali chief Ivan Maslov.
Meanwhile its overall boss Yevgeny Prigozhin has accused Russia's defence ministry of failing to provide his personnel with weapons and ammunition for operations in Ukraine.
Wagner has led Russia's offensive in the Ukrainian city of Bakhmut, though it began withdrawing on Thursday in order to hand control over to the Russian military.
The US accusations suggest it might be trying to exploit the abundance of arms in Mali. The country saw an influx of weaponry after the fall of Muammar Gaddafi in Libya in 2011, as mercenaries fighting for the former leader returned home.
Earlier this year, the US designated Wagner as a transnational criminal organisation. Prigozhin and other Wagner leaders are already subject to sanctions.
The group has been providing Mali's military government with assistance in the fight against Islamist insurgents.
Mr Maslov is seen as a key figure in Wagner, working with Malian officials to build Wagner's presence.
"The Wagner Group's presence on the African continent is a destabilising force for any country that allows for the deployment of the group's resources into their sovereign territory," the US Treasury Department statement said.
Wagner committed widespread human rights abuses and appropriated natural resources, it added.
The Treasury also suggested Wagner might be "seeking to transit material acquisitions for Ukraine through Mali" and was "willing to use false paperwork for these transactions".
The statement also accused Wagner of supplying Sudan's Rapid Support Forces with missiles for its conflict with the Sudanese army.
Russia has been seeking to expand its influence in Africa as it seeks new allies in the war with Ukraine.
Its involvement in West Africa predates the war, but evidence suggests Wagner's operations there have not been any more successful than those of other forces, such as former colonial power France.
France withdrew its troops from Mali in February last year following disagreements with the military government which seized power in 2020.