From a hideout deep in rebel territory, South Sudan’s fugitive former vice president, Riek Machar, is mobilizing insurgent forces with the aim of attacking an oil-rich area called Paloch.

Mr. Machar, alternately seen as the main protagonist or antagonist in South Sudan's crisis, is massing fighters from his Nuer ethnic group, including a feared militia known as the White Army.

Their target, Paloch, in Upper Nile state, is the only operational, oil-producing zone in this new East African nation that last December suddenly imploded, after a power struggle in the capital of Juba disintegrated into brutal civil and ethnic strife that has killed thousands.

In December, fighting halted lucrative oil production in South Sudan’s Unity state region and spurred the departure of foreign oil engineers. Analysts believe Machar's plan for Paloch is to create enough havoc to force foreign oil workers to decamp from there as well. That would drastically reduce the flow of oil, thus starving President Salva Kiir of funds but also prolonging a war that so far has shown no sign of abating.

“We want to take control of the [Paloch] oil field,” the rebel top commander said from his sanctuary of grass-roofed huts in the Upper Nile region. “This is our oil.”

Designs on Paloch are part of Machar’s strategy to control three states, two of which possess crude oil, and Juba, says John Young, a Canadian scholar who has written on the history of South Sudan’s independence movement.

The South Sudan crisis sparked after Mr. Kiir accused Machar, his former deputy, of plotting to topple him in a coup. Machar and other leading members of the ruling Sudan People’s Liberation Movement had been challenging what they said was Kiir’s increasingly autocratic leadership.

After the coup accusation and breakout of violence, Machar fled from Juba into Nuer territory as the conflict took on an ethnic coloration between Nuer and Dinka populations. Kiir is a Dinka.

During January and February, Machar fought troops from Sudan and Uganda sent to curb Machar’s ambition. However, those ambitions, including Machar’s plan to control oil producing areas, face stiff logistical and political challenges, say analysts.

Machar says he currently has limited resources and relies on armed Nuer civilians, defectors from the Sudanese Army, and on captured equipment.

Mr. Young, the scholar, says the coalition of rebel Nuer commanders allied to Machar is fragile, and East African governments like Uganda, Ethiopia, Kenya, and Sudan have been supporting the Kiir government, albeit with different levels of ardor.

A visit to Machar's hideout

To access rebel-held areas, visitors gather at dusk on the banks of the Baro River in the east of Upper Nile state. Armed Nuer men wait at a border crossing and also welcome compatriots returning from Ethiopia. They assign various travelers to jeeps and pick-up trucks for the bumpy cross-country drive to Nasir town.

Machar himself greets reporters under the shade of a tree surrounded by guards and aides. He wears a dark green combat uniform and canvas boots, appears friendly and relaxed, and puts aside a tablet computer and a satellite phone.

In a 40-minute talk, he says his troops are drawn from “those who defected from government … this is regular army, they form the core of our forces.… Then what you call the White Army, we call local defense forces, they also are a component."

Machar and his allies have spent the past month rallying support in Upper Nile among local men; the White Army appears to be thronging in Nasir.

"Because of incidents that took place in Juba [in December],” he adds, “the population rose in protest [and] these areas are organized into military formations as a tradition. They are big numbers, good enough to carry the baton forward."

Young argues that influential Nuer commanders and White Army fighters are currently allied with Machar only out of “tribal solidarity” and convenience. “There really isn’t anybody else that can play the role Riek can play,” Young says, adding that the rebels will likely split once war recedes.

In downtown Nasir, a rebel stronghold, barbershops operate out of shacks lined with tarpaulins once owned by the United Nations Refugee Agency. Power comes from antiquated generators spluttering on the roadside. There’s no mobile-phone network; fuel is scarce.

While the war appears popular in the region, it also seems to be running on fumes. Young men head into combat with only a handful of bullets; several fighters are needed to jumpstart a flatbed truck when visitors depart Machar’s well-kept compound. A 16- mile journey to Nasir from the border takes more than two hours due to a broken fuel pump.

Recent trends suggest fighting will intensify despite the efforts of regional mediators to broker a peace deal that has been under negotiation in Addis Ababa, the capital of Ethiopia.

Currently part of the war between Kiir’s Army and the insurgents – most of whom see Machar as their leader – is a battle for control of Malakal, capital of the Upper Nile.

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Machar says his attack on the oil fields will begin after the battle for Malakal ends.

East African states will see to it that Machar never gets to control the last oil field, according to analysts, since the fall of the Kiir government would risk inciting further conflict in the volatile region.