TRIPOLI, Libya — The casualties at the Aziziya field hospital south of Tripoli used to arrive with gaping wounds and shattered limbs, victims of the haphazard artillery fire that has defined battles among Libyan militias. But now medics say they are seeing something new: narrow holes in a head or a torso left by bullets that kill instantly and never exit the body.

It is the work, Libyan fighters say, of Russian mercenaries, including skilled snipers. The lack of an exit wound is a signature of the ammunition used by the same Russian mercenaries elsewhere.

The snipers are among about 200 Russian fighters who have arrived in Libya in the last six weeks, part of a broad campaign by the Kremlin to reassert its influence across the Middle East and Africa.

After four years of behind-the-scenes financial and tactical support for a would-be Libyan strongman, Russia is now pushing far more directly to shape the outcome of Libya’s messy civil war. It has introduced advanced Sukhoi jets, coordinated missile strikes, and precision-guided artillery, as well as the snipers — the same playbook that made Moscow a kingmaker in the Syrian civil war.