Russia Dominated Syria’s War. Now It’s Sending Mercenaries to Libya.

But on the ground, the war is between militias with fewer than 400 fighters typically engaged on both sides at any time. The fighting happens almost exclusively in a handful of deserted districts on the southern outskirts of Tripoli, while in neighborhoods just a few miles away, streets are clogged with civilian traffic and espresso bars bustle amid heaps of uncollected garbage.

“There is a huge discrepancy between the Libyan fighting on the ground and the advanced technology in the air from the meddling foreign powers,” said Emad Badi, a Libyan scholar at the Middle East Institute who visited the front in July. “It’s like they are different worlds.”

On a recent tour of the front-line district of Ain Zara, a Tripoli militia officer, Muhammad el-Delawi, passed out stacks of cash to fighters in T-shirts or mismatched camouflage uniforms, some in tennis shoes or sandals, others only with bare feet. The twisted wreckage of an ambulance hit by a drone missile sat by the side of the road.

The arrival of the Russian snipers is already transforming the war, Mr. el-Delawi said, recounting the deaths of nine of his fighters the previous day — one of them shot in the eye.

“The bullet was as long as a finger,” he said.

One European security official said the absence of exit wounds, a mark of hollow-point ammunition, matches injuries inflicted by Russian snipers in eastern Ukraine.

By the beginning of April, the conflict had largely died down and the United Nations secretary general, António Gutteres, arrived in Tripoli to try to finalize a peace deal. But the next day Mr. Hifter launched a surprise assault on the capital, restarting the civil war.

Officials of the Tripoli government say Russia is now bringing in more mercenaries by the week.

“It is very clear that Russia is going all in on this conflict,” said Gen. Osama al-Juwaili, the top commander of the forces aligned with the Tripoli government. He complained that the West was doing nothing to protect that government from the foreign powers determined to push Mr. Hifter into power.