General Khalifa Haftar's forces have been trying to take the capital
The US has accused Russian Wagner group fighters of laying landmines and explosives in and around Libya's capital, Tripoli.
US Africa Command (Africom) on Wednesday said it had "verified photographic evidence" that Wagner group "indiscriminately placed booby-traps and minefields around the outskirts of Tripoli down to Sirte since mid-June".
"The Wagner Group’s irresponsible tactics are prolonging conflict and are responsible for the needless suffering and the deaths of innocent civilians," Africom director of operations Major General Bradford Gering said in a statement.
There has not been any immediate reaction by Wagner Group or Russia, which has repeatedly denied involvement in Libya.
A UN report leaked in May had said hundreds of mercenaries from Wagner Group were operating in Libya. They were supporting renegade general Khalifa Haftar's battle against the Tripoli-based government, it said.
Libya has been wracked by war since the 2011 uprising that ousted long-time strongman Muammar Gaddafi.