Ghassan Salame made the remarks during a UN Security Council meeting on Wednesday.
“The reported recent arrival of thousands of mercenaries into the country risks the further extension and escalation of the conflict,” Salame said.
The Lebanese diplomare added that Libya’s conflict has been worsened by frequent violations of an arms embargo imposed in April by all parties in the war, as well as outside actors.
“The Panel of Experts is reportedly investigating over 40 cases [of violations of the arms embargo] of varying magnitude, despite non-cooperation by most of the perpetrator member states,” he said.
Violence in Libya escalated when rogue general Khalifa Haftar’s self-styled Libyan National Army launched an offensive on April 4 to seize Tripoli from the country’s UN-recognised Government of National Accord (GNA).
The two sides have since been embroiled in a stalemate on the capital’s southern outskirts.
Fighting over the last four months has killed 1,093 people and wounded 5,752, according to the World Health Organization.
Some 120,000 have been displaced over the same period.
Libya has been mired in chaos since a NATO-backed uprising that toppled and killed dictator Muammar Gaddafi in 2011.