In Chad, rebels say they have taken the eastern town of Biltine, some 750km from the capital, N’Djamena.
After attacks on Am Dam and Goz Beida, Biltine is the third town the rebels claim to have taken in recent days.
As they seek to topple president Idriss Deby, rebels have said they intend to advance towards the capital.
No immediate reaction came from the government, or an independent confirmation that Biltine had fallen.
Rebels had reached president Deby’s palace in February, before being repelled by government forces.
Sudan and Chad are fightinh a proxy war through each other’s rebel groups, said the UN. Numerous peace deals have been signed by the two countries, but they have never held.