A spokesperson for the SPLA-IO told The New Arab they would not accept any oil drilling in their territory until after fighting had ended - accusing the government of prolonging the civil war with its oil revenues.
"We repeatedly warned the company and international workers in the oilfield to leave immediately before their lives fell into risk," said William Gatjiath Deng.
Nigeria's Oranto Petroleum secured the deal, gaining exploration rights to a 25,150 square kilometre area of Upper Nile State referred to as Block B3, on March 6.
"We believe the petroleum resources of Block B3 are vast," said South Sudan's Minister of Petroleum Ezekiel Lol Gatkuoth.
The area in question is not fully under the government's control however - as rebel fighters have been engaged in some of the country's most bitter fighting there for months.
In response to Oranto's announcement, the SPLA-IO ordered "all national and international oil workers to immediately leave and evacuate" the oil fields in South Sudan.
"The brutal and ruthless regime in Juba is using billions of US dollars generated from the oil production and sale for purchasing more lethal arms," the rebels said in a statement.
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Experts warn that the continued exploitation of South Sudan's resources is one of the biggest reasons the civil war has lasted so long - leading to one of the worst man-made catastrophes of our time.
"The history of conflict and mass atrocities in Sudan and South Sudan is driven in large part by unchecked greed, manifesting itself primarily in the accumulation of wealth and power by the country's leaders," reads a new report by the Enough Project, a human rights NGO.
A famine was declared in parts of South Sudan on February 20. This was later attributed almost entirely to the government and its continued violence against its own citizens.
The Enough Project's new report, titled "How the world's newest country went awry", documents how the country's war-lords directly profit from massive government projects - feeding the money straight back into the sale of arms.
"The competing kleptocratic factions are fighting over a lucrative prize: control of the state, which in turn brings control over oil and other natural resource revenues."
South Sudan derives 97 percent of its budget revenue from sales of oil, according to a UN panel of experts. From late March to late October 2016, oil revenues totalled about $243 million.
This money is largely used to invest in weapons for the country's army - accused of rampant war-crimes and potential genocide by a recent UN report.
Yet despite frequent and repeated warnings coming from NGOs and independent inspectors, foreign investors routinely return to invest in Juba.
In February, the king of Morocco promised to pay $5 million for a project to relocate the country's capital to a new area further north.
A representative for the Joint Monitoring and Evaluation Commission (JMEC), the organisation responsible for monitoring the country's peace agreement, did not respond to a request for comment.After gaining independence from Sudan in 2011, South Sudan descended into war in December 2013, leaving tens of thousands dead and 3.5 million people displaced.