By Hereward Holland
GOK MACHAR, South Sudan (Reuters) - Teresa Abuk was boiling tea in the market of Kiir Adem, a town astride the de facto border between Sudan and South Sudan, when a white aircraft flew overhead.
Everyone panicked. Some ran, others fell to the ground. A minute later the plane returned and dropped at least three bombs, injuring Abuk's seven year-old daughter, she said.
"The pieces from the bomb exploded and the metal hurt my child's elbow and back," she told Reuters in a hospital in Aweil, capital of South Sudan's Northern Bahr el Ghazal state.
Sudan, once Africa's largest country, was carved in two in July 2011, but nearly a year and a half later the new nations are still quarrelling over where to draw the frontier.
The November bombing in Kiir Adem was a reminder that lingering hostility could yet torpedo a fragile peace, despite some progress in high-level talks between the two governments.
Conflict between the old civil war foes over the border, migrants and minerals has already done huge damage to both economies and brought them to the brink of all-out war in April.
With both sides seeking to placate domestic hardliners who resist concessions, compromise has been hard to reach. Several contested areas produce oil and are thought to hold deposits of copper and uranium, further raising the stakes.
The two sides agreed in September to withdraw their armies 10 km (6 miles) from the border to ease tensions and end an 11-month shutdown of South Sudan's oil industry, closed off in a row over how much it should pay to export through Sudanese territory.
Two weeks later, just as crude exports were scheduled to flow again, South Sudan accused Khartoum of demanding the South disarm rebels in Sudan before switching the oil back on. South Sudan's President Salva Kiir called it an "impossible mission".
Meanwhile, a dozen bombs fell on Kiir Adem, killing seven people, according to South Sudan's army. Sudan denied bombing the town, but said it had attacked rebels inside Sudan.
Both sides have been meeting in Khartoum this week to try to break the deadlock. South Sudan's chief negotiator said on Sunday oil exports could still resume by the end of the year.
But analysts say it will take much longer to bring full peace to the border. The two sides are still deeply mistrustful of one another after the decades-long civil war ended by a 2005 peace deal that paved the way for South Sudan's secession.
A TANGLED CONFLICT
Kiir Adem sits on the northern edge of a 14 mile-wide strip of land along the 1,800 km border. It is typical of several border regions where the rivals have bartered territory for other concessions, often overriding local interests.
As with much of the frontier, the annual migration of the Sudanese Rezeigat and Misseriya tribes to South Sudan complicate rights, ownership and identity in "Mile 14," as the area is called.
During the dry season, the pastoralists drive their cattle south through areas populated by Dinka, who identify as South Sudanese, to seek pasture and trade.
At the end of the civil war, Sudan and the semi-autonomous South agreed to define the border according to boundaries set up by British colonial administrators before independence in 1956, but they have failed to find a map from the agreed period.
South Sudan presented a 1954 map showing Mile 14 was populated by Dinka Malwal. Khartoum was quick to point out the map also showed the land administered as part of Darfur, placing it in northern Sudan.
It is a tender issue for both sides. As part of the September deal, the South agreed to pull its troops from Mile 14, sparking protests from the Dinka Malwal tribe who feared their ancestral land would be traded.
Sudan's armed forces agreed to keep their positions several miles away from the northern edge of Mile 14, a frontier defined by the Kiir River, or Bahr el Arab as it is known in Sudan.
GOODS OR GUNS?
Demilitarizing the border should quell hostilities, but analysts say the two sides need to adapt a porous or "soft border" to ease the movement of people and goods.
"The freedom of movement is much more important than where the border lies," said Jok Madut Jok, executive director of the Sudd Institute, a policy research group based in Juba, the capital of South Sudan.
But in a climate of mistrust, with both sides trading accusations of supporting each other's insurgents, neither government is likely to accept a porous border while security issues are unresolved.
"A soft border means the movement of people and goods across, which is a tricky issue because guns and support can cross the border more easily," said one foreign official working on border issues who asked not to be identified.
Such an approach would probably satisfy local communities. Some Dinka Malwal and Rezeigat leaders have already started charting their own course for peaceful ties.
"The British made the border. It's on the map, but it's not on the ground," Mohammed Ali Urashi, a Rezeigat representative, told Reuters at a meeting of local leaders in Gok Machar.
One aid worker estimated some 5,000 Rezeigat herdsman had brought around 100,000 cattle to graze south of the border last year despite bilateral tensions. They hope to do the same this year, but its success hinges on dispelling insecurity fears.
Still, Urashi said the Dinka and Rezeigat have managed to foster strong trade and blood relations, despite the civil war and national politics.
"For the (Sudanese) government, their intention is to fight. For us, our intention is different, it is for peace."
(Editing by Alexander Dziadosz and Paul Taylor)