24 July 2012 Last updated at 17:20 GMT
There has been renewed fighting between the Sudanese government and rebels from the Darfur region's Justice and Equality Movement (JEM).
Both sides confirmed that there had been clashes, but gave conflicting versions of events.
Sudan's army said more than 50 rebels had been killed as they were driven out two areas of East Darfur, while the JEM said it had taken control of three towns near the Abu Jabra oilfield.
The Darfur war first broke out in 2003.
It continues to this day, with Sudan accusing the new nation of South Sudan of supporting various Darfuri rebel groups.
The South Sudanese leadership in Juba denies the charge.
Col Khalid Sawarmi from the Sudanese army issued a statement saying that 50 of the rebels had been killed in Monday's clashes, and many others were wounded.
He alleged that the remaining rebels had attacked the town of Tabun and fled in the direction of South Sudan after being pushed out of East Darfur state.
But the rebels tell a different story, alleging that they took Tabun and two other towns near the Abu Jabra oilfield.
The oilfield is in the disputed region of South Kordofan, just over the state border from East Darfur.
The BBC's James Copnall in Khartoum says the apparent fighting in South Kordofan highlights the extent to which JEM is now operating outside its original Darfuri bases.
The group recently signed an agreement with other Darfuri rebels as well as fighters from SPLM-North, which operates in the South Kordofan and Blue Nile border states.
When South Sudan seceded from the north last year, rebels in those states found themselves stranded on the north side of the border in Sudan.
There has been fierce fighting between rebel groups and the Sudanese military since then, sending hundreds of thousands of refugees fleeing over the border to camps in South Sudan.
The renewed fighting in Darfur comes as the leaders of Sudan and South Sudan are meeting in Ethiopia to try to resolve bitter disputes ahead of a UN deadline on 2 August.