The UN report published on Tuesday named five Sudanese and four Chadian armed groups, which it said contributed several thousand combatants to both sides of the civil war.
But it did not mention the presence of Russian mercenaries – who were recently identified in their hundreds in media reports as fighting in the conflict.
Russia has denied that private military contractors are supporting renegade military commander Khalifa Haftar who launched an April offensive to seize the capital, Tripoli, from armed groups backing the internationally-recognised Government of National Accord (GNA).
Libya has been in turmoil since a civil war in 2011 toppled longtime ruler Muammar Gaddafi, who was later killed by rebels.
In the chaos that followed, the country was divided with a weak UN-supported administration in Tripoli overseeing the country’s west, and a rival government in the east aligned with the Libyan National Army (LNA) led by Haftar.
Despite no mention in the UN report, a diplomat – who spoke on condition of anonymity – said it is “an open secret that large numbers of Russian mercenaries are fighting in Libya”.
The reason the Russians were not mentioned in the document is that their activities have “largely taken place since the cut-off date for compiling the report”, he said.
“However, we are aware the panel are in the process of gathering evidence of the extent of Russian activity and will update the committee in the coming months,” the diplomat said.
A summary of the report, seen by AFP news agency, said Jordan and the United Arab Emirates (UAE) have regularly supported Haftar’s forces with Turkey backing the GNA in violation of a UN arms embargo imposed on Libya since 2011.
Turkish President Recep Tayyip Erdogan said on Tuesday his country was ready to send troops to Libya in support of the GNA if Tripoli requested it.
The UN report noted that military materials made by the United States, Russia and China appear to be in use in the conflict, but do not appear to have been supplied by any of those countries directly.
“Both parties to the conflict received weapons and military equipment, technical support and non-Libyan fighters in non-compliance with the sanctions measures related to arms,” the report said.
UN investigators said in the 376-page report that counterterrorism operations in Libya against the Islamic State of Iraq and the Levant (ISIL or ISIS) and al-Qaeda members by the government and Haftar’s forces continue to disrupt both armed groups and reduced their capacity to conduct operations.
However, they reported a new focus on Libya by ISIL, quoting a video in July by their leader in Libya, Mahmud Massud al-Baraassi, also known as Abu Musab Allibi, “in which he highlighted that Libya was now one of the main axes of future ISIL operations, which are designed to compensate for the loss of ground” in Syria.
“ISIL in Libya finances its activities through robbery, kidnap for ransom, extortion of Libyan citizens and the cross-border smuggling of artefacts and other commodities,” the report said.
“Taxation of human trafficking networks continues to be a source of funding for ISIL in Libya.”