Once again the disputed and oil-rich borderland area of Heglig is at the centre of a confrontation between Sudan and the newly-independent South Sudan, giving rise to renewed fears of a resumption of all-out war.
The African Union's (AU) Peace and Security Council has described South Sudan's occupation of Heglig as illegal, saying it lies north of the 1956 border which Juba and Khartoum agreed - in a 2005 accord (Comprehensive Peace Accord - CPA) that ended decades of civil war - would be their common frontier should the south eventually secede, which indeed it did in July 2011.
Sudan has warned its neighbour of strikes deep inside its territory if it fails to withdraw from Heglig, which South Sudan also claims.
UN Secretary-General Ban Ki-moon has spoken directly to South Sudan's president, Salva Kiir, also to urge a withdrawal.
On 12 April, the Security Council described the crisis as a “serious threat to international peace and security", saying it “threatens to return both countries to full-scale war and the period of tragic loss of life and suffering, destroyed infrastructure, and economic devastation, which they have worked so hard and long to overcome."
For its part, South Sudan has accused Sudan of repeatedly bombing its territory since November and of dropping five bombs on Bentiu, the capital of Unity State, on 12 April. That day, South Sudan President Salva Kiir addressed parliament in his capital, Juba.
"I always say we will not take the people of South Sudan back to war, but if we are being aggressed like this we will have to defend ourselves," he said.
"I am appealing to the citizens of the Republic of Sudan, especially the mothers, not to allow their children to be dragged into a meaningless war."
On 13 April, South Sudan said it would withdraw its forces from Heglig if it received guarantees the area would no longer be used to attack its territory, or if the UN deployed neutral forces there “until a settlement between the two parties is reached”.
Where is Heglig?
More pertinently, does it lie in Sudan, or South Sudan? Despite the AU's indignation, the answer to this question is far from clear-cut.
Heglig sits close to the middle of the 1,800km border between the two countries, but key parts of the border have not, despite CPA provisions for negotiations, yet been delineated, let alone demarcated and there are insufficient historical records (because of widespread population displacement during the development of oil installations) or living memories to easily identify the path of the 1956 line.
According to John Aswhorth, an analyst with decades of experience in the Sudans, “it is widely acknowledged that the current border is NOT the 1956 border. Successive Khartoum governments have pushed the border southwards, particularly since the discovery of oil in the 1970s.”
US-based author and longtime Khartoum critic Eric Reeves warned that “present international responses work to ensure that this [Heglig] part of the disputed border becomes a cartographic fait accompli.”
Heglig lies between Abyei, another disputed area, and the Nuba Mountains of Sudan's South Kordofan State, where, since June 2011, government forces have been battling insurgents (SPLA-N) with links to the former rebels now in power in Juba.
Heglig is also close to the border town of Jau, which was captured in late February by the SPLA-N.
During the negotiations that led to the 2005 CPA it was agreed that Heglig (known as Panthou by southerners, who claim it had always been in Unity State) would be included in Abyei, one of the "Three Areas" (along with South Kordofan and Blue Nile) whose north-or-south status was not fully resolved by the accord. Despite this lack of resolution, Abyei has been occupied by Sudanese troops since May 2011 and has not had the CPA-mandated referendum to determine its future. More than 100,000 Abyei residents who fled in May remain displaced in South Sudan.
After Khartoum rejected the initial boundaries of Abyei defined up by an international commission, these were redrawn in 2009 by the Permanent Court of Arbitration in a ruling that considerably shrank the area and excluded Heglig.
Although this court made no determination on the path of the north-south border, Khartoum insisted the ruling left Heglig in its South Kordofan State, an interpretation the AU now seems to share.
South Sudan, which says it is open to negotiations on the issue, insists Heglig lies south of the border, in its Unity State.
Why is Heglig so significant?
Links can be drawn between the latest escalation and key issues that remain unresolved since the CPA was signed: border demarcation, oil-revenue sharing and the Three Areas. (Abyei residents, for example, were supposed to decide in a referendum in 2011 whether to join the south but this has yet to take place).
Sudan lost some three-quarters of its oil supplies when South Sudan became independent. Since then, Heglig has accounted for about half of Sudan’s daily output of 115,000 barrels, although production is currently halted.
The latest clashes also threaten an important agreement Juba and Khartoum signed in March 2012 that would have made it easier for hundreds of thousands of southerners to remain in Sudan. Without that deal, they were supposed to regularize their status - logistically almost impossible - or leave by 8 April. South Sudan is ill-equipped to accommodate such a sudden and large influx, especially because the imminent rainy season will render most roads impassable.
Veteran Sudan analyst John Ashworth told IRIN: "I don't want to say that the CPA was flawed, because it was the best that could be hoped for at the time, but we are certainly now reaping the fruits of areas not fully addressed by the CPA."
According to historian and Abyei expert Douglas Johnson, none of the international players involved in the CPA gave much thought to what would happen to the Three Areas in the event of secession because "they were initially entirely focused on trying to make unity appear attractive." Once the independence writing was on the wall, "they were only concerned with ensuring that independence was peaceful."
Mukesh Kapila, who served as UN humanitarian coordinator in Sudan in 2003 and 2004 and now works for the Aegis Trust, an advocacy NGO, told IRIN: "The CPA fudged-over the legitimate complaints of the long-suffering marginalized people of Nuba, Abyei, Blue Nile, and Darfur. Unless a sincere attempt is made to solve this in a fair and just manner, violent conflict will continue to erupt here and there. Citizenship, oil, and border demarcation may complicate the picture but they are, in significant part, proxies for the grievances of the much abused people of Sudan's borderlands which have to be tackled first if there is to be any peace and stability for the two countries."
*This is an updated and revised version of "SOUTH SUDAN: Briefing on Heglig clashes" published on 29 March
This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information: https://shop.un.org/rights-permissions