Khartoum has vowed to recapture a disputed oil field as fighting along the border between the two Sudans threatens to turn a rancorous divorce into an all-out war.
Reporters who reached the oil outpost of Heglig yesterday described the wreckage left by a northern retreat, with soldiers' bodies strewn along the roads.
The division of Africa's biggest country in June last year has been followed by pitched battles along the disputed frontier, which have escalated in recent weeks as northern bombers have raided targets inside South Sudan, while southern troops have marched into territory previously held by Sudan.
The fighting has derailed efforts at an internationally brokered settlement meant to divide citizens, territory and natural resources between the two former civil-war foes.
The latest front to emerge is at Heglig, which had remained under the control of the north since the countries' separation.
The government in the southern capital, Juba, has been criticised by much of the international community for its "illegal occupation" of the area since its troops drove out the Sudanese Armed Forces (SAF) last week.
Northern authorities have successfully argued that the oil fields were separated from another disputed enclave, Abyei, by the Permanent Court of Arbitration in 2009 and placed under the control of the northern state of Southern Kordofan.
The government of Omar al-Bashir has denounced the seizure of Heglig and Sudan's parliament voted on Monday to declare South Sudan an "enemy state" and insisted southern forces must withdraw before any talks can take place.
However, Juba has its own claims to Heglig and says the area's separation from Abyei does not change the fact that its permanent status is contested and can only be settled by a permanent demarcation of the border.
John Ashworth, a Sudan expert, said that the international response to the occupation of Heglig has been one-sided: "Heglig is disputed. Both sides believe they have a legitimate claim, and the international community should refrain from making statements about Heglig's status until demarcation of the disputed border has been completed."
The UN confirmed bombs had been dropped near one of its sites at the weekend, and expressed concern at a build-up of militia forces in the northern-held border enclave of Abyei.
The loss of the Heglig fields, which supply roughly half of Sudan's oil, has shocked many in the Arab-dominated north, which is already suffering from runaway inflation and rumblings of political dissent.
During the two decades of civil war that ended in 2005, the SAF was accustomed to militarily dominating the southern-led guerrilla army, the SPLA.
Khartoum retains control of the skies with a mixture of Soviet-era bombers and MiG fighter jets but its former recruiting grounds in the Darfur region and the Nuba Mountains are running dry and the government faces rebellions in those areas. On the ground, the SAF has been pushed back repeatedly.
There are still hopes that the war will not spread beyond the border areas and that the neighbours will return to the negotiating table, but Juba has made two bold moves this year – shutting down oil production and seizing Heglig – suggesting it may be more ready for war than some thought.
The south is even more dependant on oil than the north, but with much of its population scattered across refugee camps in one of the least developed countries in the world, southern leaders may gamble that their people have less to lose than the city dwellers in the more developed north.Reuse content