JUBA // With the northern Sudanese army's invasion of the disputed border region of Abyei, Africa's largest nation has inched back towards civil war.
Since an on-and-off, 50-year war that cost some 2.5 million lives and ended with a peace accord in 2005, ties between north and south have been peaceful, if occasionally tense.
Now the uneasy peace could unravel just as the south stands poised on July 9 to become the world's newest nation, after a referendum in January saw people vote to secede.
The current crisis is a sign of the "enormous pressures" on both the central government in Khartoum and the soon-to-be government of South Sudan, said Eddie Thomas of the Rift Valley Institute.
The invasion has halted talks between the two sides aimed at working out the details of southern secession - including oil-sharing.
Abyei, the latest flashpoint between north and south, is a fertile grazing region and the source of 75 per cent of the country's 500,000 barrels a day of oil production.
The renewed violence was in some ways predictable.
The 2005 peace deal promised Abyei residents their own referendum over whether to join the north or south, but that never took place as neither side could agree who was qualified to vote.
A World Court ruling two years ago left Abyei's most lucrative oil fields part of the north, but the area's new borders have never been demarcated due to security concerns, leaving the issue for all practical purposes in doubt.
Hedging their bets on peace, both Khartoum and Juba maintained military units there in recent years instead of forming and deploying a joint north-south force, as promised by both sides.
The latest crisis began last week when southern troops attacked a column of northern and United Nations troops moving away from Abyei, according to the UN.
In response, northern forces moved tanks into the town of Abyei over the weekend, leading to looting and burning by armed groups. Since then, more than 15,000 people have fled the region to the south, UN officials said yesterday.
To protest the north's invasion and takeover of Abyei, a minister of cabinet affairs for the government in Khartoum also resigned yesterday.
Luka Biong Deng, who hails from the south, said the government of Omar al Bashir had declared Abyei a "northern town" and had dismissed international calls to pull its troops out of the district.
"We had hoped that we could form two viable states in good relationship with each other, but those in Khartoum do not seem interested in peace," Mr Biong Deng said.
"But with war crimes being committed in Abyei at the hands of the [Khartoum's ruling] National Congress Party, I could not in good faith continue to take part in such a government," he said.
Sudan's government insisted yesterday that a new impasse over the Abyei region should be resolved through peaceful means.
"There's no way of going back to war," Kamal Ismail Saeed, Sudan's ambassador to Kenya, told reporters yesterday in Nairobi.
Nonetheless, Mr Thomas of the Rift Valley Institute said the crisis is a "very serious departure" from the often insecure, but until recently, still functioning relationship between Sudan's north and south.
The UN and western governments have condemned Khartoum for its invasion of Abyei, but one Western diplomat in the southern capital of Juba said that northern forces were unlikely to heed the calls for their withdrawal. The international community, he said, had little leverage in Khartoum.