Russia recently sent fighter jets to Libya to support Russian mercenaries fighting for strongman Khalifa Haftar, the U.S. military command for Africa (Africom) said Tuesday, in a major escalation in the long-running conflict

The military fighter aircraft left Russia and first stopped in Syria where they “were repainted to camouflage their Russian origin” before arriving in Libya, said Stuttgart-based Africom.

The U.S. military did not specify when exactly the jets arrived, only saying that it was “recently”.

The announcement comes a day after Libya’s UN-recognised government said hundreds of Russian mercenaries backing rival military commander Haftar had been evacuated from combat zones south of the capital Tripoli.

The retreat follows a series of setbacks for Haftar’s years-long offensive to seize the capital from the Tripoli-based Government of National Accord (GNA).

The Kremlin has always denied involvement in the conflict.

But United Nations experts said in a report last month that the Wagner Group, a shadowy Russian paramilitary organization seen as close to President Vladimir Putin, had sent fighters to back Haftar.

“For too long, Russia has denied the full extent of its involvement in the ongoing Libyan conflict. Well, there is no denying it now,” said U.S. Army General Stephen Townsend in the Africom statement.

“Russia is clearly trying to tip the scales in its favour in Libya,” he added. 

“Just like I saw them doing in Syria, they are expanding their military footprint in Africa using government-supported mercenary groups like Wagner.”

He described the Russian warplanes deployed to Libya as “fourth generation jet fighters”.

Oil-rich Libya plunged into conflict after the ouster and killing of veteran dictator Moamer Kadhafi in a 2011 NATO-backed uprising, with rival administrations and militias vying for power.

The conflict worsened when Haftar, who is also backed by Egypt, the United Arab Emirates and Saudi Arabia, launched an offensive on Tripoli in April 2019.

Africom said Russia’s actions risked prolonging the conflict and exacerbating “casualties and human suffering on both sides”.

If confirmed, Russia’s fighter jet deployment would constitute another violation of a much-abused 2011 UN arms embargo.

World leaders agreed in January to uphold the embargo and stop meddling in the conflict that has dragged in major regional rivals.

But the UN has repeatedly warned that both sides have continued to receive arms and fighters.