The Arab League has said it will hold an emergency meeting over renewed violence between Sudan and South Sudan.
Ahmed bin Helli, deputy secretary-general, said on Thursday that the meeting, requested by Sudan, will bring together the regional bloc's foreign ministers and will be held next week in Cairo, the Egyptian capital.
Sudan and South Sudan have clashed over Heglig, an oil-rich region that accounts for about 50 per cent of Sudan's oil production and is currently occupied by troops from the south.
South Sudan, which gained independence last July after voting in a referendum to secede from Sudan, claims it occupied Heglig after it was attacked by the Sudanese army.
It has so far ignored calls by the international community to pull its troops out, saying it is defending its territorial integrity.
Ban Ki-moon, the UN secretary-general, has called the south's seizure of Heglig an "illegal act" and urged the two nations to negotiate to avoid all-out war.
Colonel Philip Aguer, the spokesperson of the South Sudan army, said the Sudanese army had carried out attacks on the south on Wednesday and on Thursday in the latest clashes.
The two the sides have never fully agreed where their shared border lies nor have they reached agreement on how to share oil wealth that is pumped from the border region.
Hague court ruling
A ruling by the Permanent Court of Arbitration in The Hague in 2009 appears to put Heglig in the Sudan's state of Southern Kordofan, which the South now disputes.
Sudan's president, meanwhile, has said he will "cut" the hand of aggressors and retake the contested Heglig region.
|In-depth coverage of North-South strife over border
Omar al-Bashir told a rally in Sudan's North Kordofan state on Thursday he would not surrender "an inch" of the country and that he would firmly deal with its enemies.
"We will not give them an inch of our country, and whoever extends his hand on Sudan, we will cut it," Bashir told thousands of people in El-Obeid, North Kordofan's capital.
"Heglig is in Kordofan," he said in the speech broadcast on state television, dancing and waving his walking stick.
Al Jazeera's Peter Greste, reporting from Bentiu in South Sudan, said neither side is willing to give way.
He said military sources inside South Sudan spoke of a "renewed outbreak of very heavy fighting at town some distance north of Heglig".
The developments come as a US envoy said on Thursday that Sudan had agreed "in principle" to allow assistance into South Kordofan, where aid workers say that hundreds of thousands could go hungry.
Princeton Lyman, US special envoy on the two Sudans, said he called on authorities in Khartoum to show that they are serious about putting an aid proposal into action, amid fears it will soon be too late due to rain.
"I pressed again for the government to prove this and prove it rapidly because the rainy season is nearly upon us. They have said yes in principle but they've got questions about its implementation," Lyman said.
Speaking by telephone from Khartoum, Lyman said that the situation "is getting worse and people are in real basic need for both food, medicines".