North Sudanese army forces have taken control of the main town in the disputed Abyei region after fighting with southern forces, both sides said.
Southerners voted in January to become independent on 9 July in a referendum agreed under a 2005 peace deal.
However, violence has escalated in recent days in Abyei, the main outstanding dispute between the two sides in the run-up to secession.
'Enemy forces' had been expelled to the south, Khartoum-based Sudanese state television said in a news bulletin after fighting was reported throughout the day in Abyei.
The disputed region has oil and fertile grazing land.
The United Nations said the northern army deployed 15 tanks alone in one area in Abyei town.
Gunshots could be heard until fighting appeared to subside for the night, spokeswoman Hua Jiang said.
Another UN official said the end of fighting before midnight indicated the north appeared to be in control of Abyei town, although the official confirmation would have to wait until patrols could take a look.
In another telling sign, Sudan's President Omar Hassan al-Bashir removed the two heads of the Abyei administration and dissolved the region's administrative council, state news agency SUNA said. It gave no explanation.
The southern army acknowledged northern forces controlled the main town.
'Abyei town is now under control of the SAF (Sudanese Armed Forces). They came with tanks,' said SPLA spokesman Philip Aguer.
He said northern aircraft had also bombed from the air and shelled at least four villages, among them Todach and Tagalei, which he said had been already hit on Friday.
Abyei residents were also meant to have a referendum in January over whether to join the North or the South.
Disputes over who could vote derailed that ballot and talks over the status of the region have stalled.
North and South have also yet to agree how to share oil revenues and other assets prior to the break-up.
