Russia has recently deployed military fighter aircraft to Libya to support Russian mercenaries fighting there, the United States military's Africa command said it had assessed in a statement on Tuesday.
"Russian military aircraft are likely to provide close air support and offensive fires for the Wagner Group PMC that is supporting the Libyan National Army's (LNA) fight against the internationally recognized Government of National Accord," the statement said.
It said the aircraft arrived from an airbase in Russia after transiting through Syria where they were repainted to camouflage their Russian origin.
Officials in Russia could not be immediately reached for comment.
The United Nations Libya mission has condemned what it calls a huge influx of arms and fighters into Libya in breach of an arms embargo.