The US military has accused Russia of deploying warplanes to Libya in support of Russian-backed mercenaries allegedly fighting for Khalifa Haftar, the renegade general commanding the Libyan National Army (LNA).
US Africa Command released photos it says show Russian fighter jets, which had travelled from Russia and transited in Syria, deploying to Libya, where they were repainted to disguise their origins.
Military intelligence tracked the "fourth generation jet fighters", presumably by satellite, as they flew to Libya, according to US Africa Command's chief Stephen Townsend.
A satellite image released by the US military purportedly shows a Russian Mikoyan MiG-29 at the al-Jufra airbase in northern Libya.
Another photo shows Russian insignia and tail markings on a military aircraft. Labels on the satellite images point out four MiG-29 aircraft and two Sukhoi Su-35 jets stationed at an airbase.
The fighter jets will be used to support an air offensive by Haftar, piloted by Russian mercenaries, flying Russian-supplied aircraft, according to the US military.
Russian officials denied that the government had sent combat aircraft to Libya, with Andrey Krasov, first deputy chairman of the State Duma Defense Committee, saying the US assertions did not "correspond to reality", according to RT, a Russian-backed news channel.
Foreign mercenaries in Libya
The UN earlier in May confirmed that mercenaries from the Wagner Group, a Russian paramilitary organisation seen as close to Vladimir Putin, were fighting in Libya.
Reports from the New York Times on investigations by the UN have also identified mercenaries from South Africa, the UK, Australia and the US taking part in operations in Libya.
Fighting between Haftar's LNA and the Tripoli-based Government of National Accord (GNA) has drawn in several countries, effectively competing in a proxy war following the overthrow of former Libyan leader Moamer Gadhafi.
The French government previously admitted carrying out air operations in Libya when three French special forces soldiers died in a helicopter crash near Benghazi in July 2016.
The UN-backed GNA last month accused France of conducting unauthorised flights over its territory, during flights over Misrata and Abu Grein, a theatre of operations further east.