Forces from eastern Libya who have swept through the south and taken control of remaining oilfields in recent weeks have now reinforced a base in the centre of the country and signalled to the capital Tripoli that it may be next, reports Reuters.
The United Nations, stunned by the southern advance, is scrambling to mediate between eastern commander Khalifa Haftar and Tripoli's internationally-recognised government led by Prime Minister Fayez al-Serraj, Western diplomats say.
They fear it may be the last UN attempt to unify the rival administrations and end the chaos that followed the overthrow of Muammar Gaddafi in 2011 with free elections.
Haftar, a 75-year-old former general, is increasingly taking the situation into his own hands, backed by the United Arab Emirates and Egypt, which see him as a bulwark against Islamists and the man to restore order.
He has not said whether he wants to march on Tripoli, which would dramatically escalate tensions. But his Libyan National Army (LNA) has hinted heavily that it might do so – if Haftar is not recognised as the country's overall military commander, his aim since he began assembling the force in 2014.
"Some military sources say the LNA will move towards Tripoli after the announcement that the south has been secured," read an item on an LNA website.
"The same sources said there is coordination with some units inside Tripoli and its suburbs for the army to enter Tripoli."
The LNA spokesman said a purported order from Haftar for troops to move, seen by Reuters and publicised by his supporters, was not genuine.
But the capital has been rife with rumours of invasion and residents have reported seeing young people driving around playing loud songs praising Haftar from their car radios.
While several LNA units returned this month to Benghazi, Haftar's power base, some units went to Jufra, a city in the desert straddling east and west, LNA sources say.
From there they could go home, or – the implied threat according to diplomats – move northwest towards Tripoli, should talks over power sharing and elections fail.
Haftar taps into fatigue among Libyans yearning for electricity, petrol and banknotes scarce in a country which once enjoyed some of highest living standards in the region.
For many, especially in the east, the general is the only one who can end fighting by myriad groups with ever-changing names. For his enemies in western cities and militants who were oppressed under the old regime, he is a new Gaddafi.