Gen. Khalifa Haftar, the rebel leader who controls Libya’s oil-rich east, recently declared he has a popular mandate to rule all of the North African nation, a move that may give Russia the upper hand if he can succeed in taking Tripoli amid nearly a decade’s worth of sectarian strife.

In the disarray since dictator Moammar Gadhafi was killed in 2011, a civil war has raged across Libya, and Islamic State remnants have secured a tenuous footing in the south. But more troubling, say defense officials and U.S. Africa Command, is that Russia has inserted a paramilitary group to support Haftar and position itself on the southern flank of NATO.