The UN said Wednesday it was "following with great concern" claims that Russia recently sent fighter jets to Libya to support Russian mercenaries fighting for strongman Khalifa Haftar in the long-running conflict.
On Tuesday, the US military command for Africa (Africom) accused Moscow of deploying several MiG-29 Fulcrum jets and Su-35 Flankers in support of Haftar, who has been fighting to seize Tripoli from the UN-recognized Government of National Accord (GNA) since April 2019.
Pentagon spokesman Jonathan Hoffman said the Russians had sent a mix of "approximately 14 military fighters."
Moscow has not reacted to the claim.
The UN Secretary General's spokesman Stephane Dujarric said that, if proven, it would "constitute a flagrant violation of the arms embargo" imposed on Libya in 2011.
Without mentioning Russia, Dujarric said "reports of violations have increased significantly in the past few weeks, with reported near-daily transfers by air, land and sea."
He added: "This increase in the violations of the arms embargo will only lead to the intensification of the fighting, which will result in devastating consequences for the Libyan people."
Oil-rich Libya plunged into chaos after veteran dictator Moamer Kadhafi was ousted in a 2011 NATO-backed uprising.
Rival administrations and militias have been vying for power ever since.
Russia and the UAE back Haftar while the GNA gets support from Turkey, whose drones and air defense systems helped deliver key victories in recent weeks.
Fighters loyal to Libya's UN-recognised Government of National Accord (GNA) climb over a partially disassembled MiG 23 aircraft, after seizing Al-Watiya airbase southwest of the capital Tripoli, on May 18, 2020.