South Sudan blamed as it gears up for war
At a dusty intersection just north of Bentiu, three young South Sudanese soldiers were waiting for a lift to the frontlines.
"We are in a process leading to war," said 24-year-old Moses Akon, thoughtfully.
Trucks and pick-ups crammed with troop reinforcements, weapons, and a surprising amount of beer - crates of Red Horse beer to be precise - raced past.
"We do not want to fight, but we shall," said Mr Akon.
The front line itself consists of shallow foxholes dug into the hard earth, tank and heavy machine guns hidden under trees, and a mood of frustration and belligerence among many of the soldiers who were forced - under the most withering international pressure - to withdraw from the Heglig oil fields they'd recently seized from Sudanese forces to the north.
"We are now at war," said Major General James Gatduel, freely admitting that he and his men are itching to advance once more to recapture Heglig.
On Saturday afternoon, Sudanese planes bombed the frontlines here, and about five minutes after we left another brief skirmish erupted as Southern forces fired on what they say were two helicopter gunships, and then came under attack from a fighter jet.
The tensions here are the result of failed diplomacy and brinkmanship during the long process that led to South Sudan winning independence last year without any final agreement on its exact borders or how to share the vast oil fields that straddle those borders, and on which both north and south now depend for their economic viability.
For years international sympathy has rested firmly with the southerners - victims of northern aggression and of a seemingly endless succession of humanitarian calamities - but in recent months South Sudan has begun to alienate many of its key backers with a series of rash reactions to northern provocations.
"Talk about shooting yourself in the foot," fumed one prominent western official, speaking on condition of anonymity, in South Sudan's capital, Juba.
"It's so frustrating - they've squandered everything in 10 months."
The South's most controversial move was to halt all oil production, after failing to agree on transit fees for the pipeline that runs north through Sudan.
Oil revenues account for some 90% of the government's budget, and the money will start to run out in six weeks.
The local currency is already under severe pressure, petrol queues are beginning to form, and President Salva Kiir's handling of a series of spiralling economic, diplomatic and military crises has left many foreign observers shaking their heads in disappointment.
And yet, in the crowded wards of Bentiu's civilian hospital, where wounded soldiers and bandaged children lie side by side, there is no sense of panic.
"We cannot share our oil - we are proud to die for it," said Karani Mayok, 28, who says he lost his left leg when a bomb was dropped from a Sudanese warplane on his village on 15 April.
"When we came to be independent from the north we knew there would be suffering, but we are ready to defend our land," said the medical director, Dr Peter Gatkuoth.
Still, he urged both sides to return to negotiations.
"We need to believe in peace. We share one name 'Sudan' in both north and south. Let us not go back to war. It is not good for all," he said.
Both Sudan and the South are reliant on their oil revenues, which account for 98% of South Sudan's budget. But the two countries cannot agree how to divide the oil wealth of the former united state. Some 75% of the oil lies in the South but all the pipelines run north. It is feared that disputes over oil could lead the two neighbours to return to war.
Although they were united for many years, the two Sudans were always very different. The great divide is visible even from space, as this Nasa satellite image shows. The northern states are a blanket of desert, broken only by the fertile Nile corridor. South Sudan is covered by green swathes of grassland, swamps and tropical forest.
Sudan's arid north is mainly home to Arabic-speaking Muslims. But in South Sudan there is no dominant culture. The Dinkas and the Nuers are the largest of more than 200 ethnic groups, each with its own languages and traditional beliefs, alongside Christianity and Islam.
The health inequalities in Sudan are illustrated by infant mortality rates. In South Sudan, one in 10 children die before their first birthday. Whereas in the more developed northern states, such as Gezira and White Nile, half of those children would be expected to survive.
The gulf in water resources between north and south is stark. In Khartoum, River Nile, and Gezira states, two-thirds of people have access to piped drinking water and pit latrines. In the south, boreholes and unprotected wells are the main drinking sources. More than 80% of southerners have no toilet facilities whatsoever.
Throughout the two Sudans, access to primary school education is strongly linked to household earnings. In the poorest parts of the south, less than 1% of children finish primary school. Whereas in the wealthier north, up to 50% of children complete primary level education.
Conflict and poverty are the main causes of food insecurity in both countries. In Sudan, many of the residents of war-affected Darfur and the border states of Blue Nile and South Kordofan, depend on food aid. The UN said about 2.8m people in South Sudan would require food aid in 2013. The northern states tend to be wealthier, more urbanised and less reliant on agriculture.