South Sudan says the northern army's seizure of the contested Abyei oil region is "illegal."
Southern Sudan's information minister, Barnaba Marial Benjamin, is calling for help from the international community. He said Sunday it is the responsibility of the United Nations Security Council to see that northern troops withdraw from the region.
The Khartoum government said Sunday the Abyei region is now under its control. The action has raised fears that a new north-south civil war will break out just as the south prepares to declare independence on July 9.
The two sides have not resolved disagreements about the future of Abyei.
Amin Hassan Omar, a minister of state for presidential affairs, said Sunday that northern forces are clearing the Abyei region of southern army troops.
North Sudan army tanks rolled through Abyei's main town, after a military offensive that scattered southern troops and sent residents fleeing for safety. Khartoum also issued a decree dissolving the town's administration.
The aid group Doctors Without Borders said nearly all of Abyei's population has fled the town since violence started escalating in recent days.
Both the United States and Britain have condemned the Sudanese government's seizure of Abyei.
Sudanese President Omar al-Bashir has warned his government would not recognize south Sudan as an independent state it it did not give up claims on Abyei.
A U.N. Security Council delegation is in Khartoum Sunday for talks on the Abyei issue.
The armies of the north and south previously had agreed to conduct joint patrols in Abyei. But, fighting erupted in the region Thursday, when a northern army convoy accompanied by U.N. peacekeepers came under attack. Both armies accused each other of firing first.
The White House accused southern Sudanese forces of attacking the convoy and deplored the incident.
The Obama administration urged President Bashir and southern Sudanese President Salva Kiir to meet "immediately" and agree on a way to restore calm, uphold their peace agreement and recommit to a negotiated political settlement on Abyei's status.
A referendum on whether Abyei should be a part of the north or the south had been scheduled for last January, but did not take place because the two sides could not agree on who was eligible to vote.
South Sudan voted overwhelmingly to split from the north in a January referendum that was part of a 2005 peace agreement. That pact ended a 21-year north-south civil war in which the Abyei region was a key battleground.