Both countries accuse each other of massing troops along border areas as negotiations over land and oil revenues near.
Tensions build between two Sudans
JUBA // As Sudan and its newly independent neighbour prepare for negotiations over land and oil revenues disputed since the south seceded, violence has exploded along the border, with leaders from both countries warning they are ready to go to war.
Analysts say recent clashes will probably not lead to all-out war, but the escalating conflict will undermine talks about issues left unresolved when the south split from Sudan after two decades of fighting.
"Of course war is possible, but I don't think it's likely," said John Ashworth, an expert on the region who has spent 28 years in Sudan and South Sudan. "This ramping up of rhetoric, which I would say is part of the negotiation process, even includes violence."
Both sides are moving troops to border areas and accuse each other of supporting rebel groups within their territories. South Sudan alleged that Sudan Armed Forces (SAF) escalated the conflict significantly by using tanks and uniformed soldiers to back up a militia assault on one of its border garrisons on Wednesday - a charge SAF denied.
Khartoum also denied carrying out the November 10 aerial bombing of a refugee camp in South Sudan, which prompted condemnations from the White House and the United Nations.
The bombing came just hours after South Sudan's president, Salva Kiir, warned that Khartoum was plotting to invade his country. He said the south did not want to go to war, but added: "We will never permit anyone to violate our sovereignty."
Mr Kiir said he decided to speak in response to accusations made by the Sudanese president Omar Al Bashir and his government in the media and in a complaint to the UN Security Council, alleging that South Sudan is backing insurgents fighting to topple the regime in Khartoum.
Sudan's state-owned news service, Suna, said the government complained that Juba was providing the insurgents with "anti-aircraft and anti-tank missiles as well as ammunition, landmines and mortars".
The rebels were formerly part of Sudan Peoples Liberation Movement, which is now the ruling party of South Sudan. Mr Kiir said his country has had no political or military relationship with them since declaring independence on July 9.
"All these accusations are actually a prelude from Khartoum to justify their pending actions against South Sudan," Mr Kiir told reporters on November 10. "Tomorrow, when Bashir invades South Sudan, then he will say ... he took the action to revenge what was being done to him."
Sudanese forces pushed the rebels out of their stronghold of Kurmuk in Blue Nile state on November 3. Three days later, Mr Al Bashir visited Kurmuk and the state capital, Damazin, where he told supporters he would go to war if Juba continued to back the insurgents.
Many say a return to war is unlikely, but the recent sabre rattling has worsened an already tense relationship.
"The consequences of renewed war outweigh any potential gains," said Zach Vertin, an analyst with the International Crisis Group. "But the longer border tensions persist and an oil deal is not agreed, the threat of escalation increases."
Oil is a key point of contention to be discussed in the next round of negotiations in the Ethiopian capital, Addis Ababa. The talks were to begin yesterday, but Khartoum pulled out late on Thursday and they have been tentatively postponed until today.
When the south separated, it took two thirds of Sudan's oil reserves; tipping the country into an economic crisis that has led to rare street protests against a government fighting spiralling inflation. The countries now must agree on the price landlocked South Sudan will pay to transport its oil through a pipeline across the north. Khartoum wants US$32 (Dh117) a barrel; Juba is offering 41 cents (Dh1.50).
Most of the oil is being pumped from states along a border that has yet to be demarcated in sections and is also up for negotiation. This week, South Sudan's army spokesman linked the two issues, accusing Khartoum of carrying out bombing raids and sending militias into oil-rich areas along the frontier.
"This is what I call an oil war," said Col Philip Aguer in an interview. "They are creating their own borders by force, by trying to occupy territory of South Sudan."
He accused Sudan of massing troops along the border with the oil-rich states of Unity and Upper Nile in preparation for further military action. Khartoum has made the same allegation against South Sudan.
Oxfam International announced on November 11 that it pulled aid workers out of two locations in Upper Nile after its staff reported seeing "bombing and heavy artillery" that day.
The Enough Project, a Washington DC-based advocacy group, said the same day that satellite imagery showed Sudan's military was upgrading airbases in Blue Nile state that would enhance its ability to carry out air strikes.