Khartoum - Rebels from Sudan's Darfur region on Thursday said they seized two Sudanese military positions north of the Heglig oil field occupied by South Sudanese forces.
In fighting on Wednesday night, the Justice and Equality Movement (JEM) took control of the outposts 40km north of Heglig, said the group's spokesperson Gibril Adam Bilal.
"Now we are surrounding the main SAF compound," Bilal said.
The spokesperson of the Sudanese Armed Forces could not be reached for comment.
Bilal said three JEM rebels died in the battle, in which they claimed to seize Sudanese vehicles and equipment, but he had no body count for the government forces.
The area is near the village of Kelet where South Sudanese troops repelled the northern army and destroyed two of their tanks last Friday, the Southern army said earlier.
Bilal denied that JEM forces were fighting alongside the South Sudanese, who occupied Heglig on April 10 and allege it was used to attack the South.
Khartoum's foreign ministry claims that international press photos show the Darfur rebel movement has been fighting with Southern troops.
Sudanese Revolutionary Front
The United Nations, the United States and the European Union have criticised the South's occupation of Heglig but have equally denounced Sudan's air strikes against the South.
There are widespread fears that the fighting will spread.
It is already the worst since South Sudan won independence in July after a 1983-2005 civil war which killed two million people.
Although South Sudan disputes it, Heglig has been internationally regarded as part of Sudan.
JEM and other key Darfuri rebels last year joined the Sudanese Revolutionary Front with insurgents from the border states of South Kordofan, where Heglig lies, and Blue Nile.
The rebels pledged to topple the Khartoum regime, which they regard as unrepresentative of the country's political, ethnic and religious diversity.