Fighting has broken out in north-eastern Sudan, where government forces are battling rebels for control of a town south of the main port.
The fighting around Tokar, some 120km (75 miles) from Port Sudan, began on Sunday. Both sides say there have been heavy casualties.
The Beja Congress, which complains of marginalisation, says it has launched its biggest offensive in years.
Officials also blame attacks on rebels from the western Darfur region.
There is no independent confirmation of the involvement of the Justice and Equality Movement, but a BBC reporter saw JEM rebels whilst visiting the border area last week.
Sudan blames neighbouring Eritrea, which supports the Beja rebels, of being behind the fighting. The clashes are a setback for peace efforts, which were boosted at the weekend when a deal was signed between the government and the biggest opposition grouping, the National Democratic Alliance.
Eastern rebels were part of the NDA alliance, which has been exiled for more than 15 years.
A peace deal was also signed early this year between the government and southern rebels, to end a 22 year civil war.
Talks are under way in Nigeria to try to end the two-year rebellion in the west, where more than two million have fled their homes in Darfur and at least 180,000 have died.
A spokesman for African Union mediators told the BBC that so far the clashes in north-eastern Sudan had not affected the negotiations.