Sudan has threatened military action against the neighbouring state of South Sudan, accusing its troops of involvement in rebel attacks along the border.
The Sudanese foreign ministry, in a statement, said the government would file a complaint with the UN Security Council and the African Union after attacks on Sunday in which Sudanese rebels said they killed 150 government soldiers along the disputed border.
Sudan's military denied the casualty toll and said it had killed a "huge number" of rebels, but gave no figure.
The deaths occurred during Sunday's "surprise attack" on a government base in the border area of Jau, Arnu Ngutulu Lodi, of the Sudan People's Liberation Movement-North (SPLM-N), told the AFP news agency.
Ethnic minority fighters in the SPLM-N fought alongside the former rebels now governing South Sudan.
The South Sudan government said it was an internal Sudanese matter and none of its forces were involved, but the reported assault fuelled tensions between the neighbours already at odds over oil exports and border disputes.
Any involvement of southern forces would have violated a non-aggression pact signed by the two sides this month.
The rebels, who last year formed a "revolutionary front" aimed at toppling Sudan's ruling elite, claimed the attack in the contested Jau area - part of an oil-rich region on the poorly defined border - as their first combined operation against government forces.
More than 360,000 people have been internally displaced or severely affected by fighting in the two Sudanese border states, the UN says.
With Sudan severely restricting the work of foreign relief agencies in the war zone, international concern is mounting over malnutrition and food shortages in the area.