Sudan's Government has ignored international appeals for a ceasefire, continuing an offensive in the country's oil-rich central provinces that threatens to push the country back into civil war.
At least 64 people have been killed and up to 60,000 people have fled bombing raids along the prospective border with southern Sudan despite calls from United States President Barack Obama for a halt to military operations.
In three weeks, Sudan will formally split in two following the January referendum in which southerners overwhelmingly voted to secede from the north. The north will lose a third of its oil revenues as the new state, South Sudan, will contain most of Sudan's oil reserves.
Most of the fighting has centred on South Kordofan, an oil-rich region on the northern side of the new border, where government forces have been accused of "ethnic cleansing". Tens of thousands of civilians have fled south or into hiding in the Nuba Mountains.
The United Nations said yesterday there was a "growing sense of panic" in the region where civilians have been trapped by fighting and northern troops have shut off humanitarian access.
Authorities in southern Sudan also accused the northern army of trying to push south from the disputed region of Abyei yesterday, overrun by northern troops last month in violation of international agreements.
Talks this week in the Ethiopian capital, Addis Ababa, ended with an agreement to withdraw all forces and send in Ethiopian peacekeepers under the UN banner. But southern military spokesman Colonel Philip Aguer said yesterday that northern forces had tried to cross the Kiir River, traditionally seen as a north-south dividing line.
The Government of Omar al-Bashir - wanted by the International Criminal Court for war crimes in the western region of Darfur where hundreds of thousands of people were killed - denies targeting civilians, insisting it has been attacked by southern armed groups.
Obama warned that there was "no military solution" to the crisis, adding: "The leaders of Sudan and South Sudan must live up to their responsibilities. The Government of Sudan must prevent a further escalation of this crisis by ceasing its military actions immediately."
Sudan has been racked by civil war since independence from Britain in 1956. Outlying populations have persistently accused the hardline Muslim central governments of systematic economic neglect and human rights abuses.