The Eastern Front accused Khartoum of preparing for an assault on its camps at a time when the leaders and cadres would be in Tripoli negotiating with the Sudanese government.
The front said that Khartoum was recruiting the Janjaweed militia in eastern Sudan as it had done in the troubled western region of Darfur where the gunmen are accused of wreaking mayhem.
An Eastern Front official told reporters: "This is a very divisive policy that pits members of the same community against each other."
Last month, the front accused the Sudanese army of attacking its camps in the eastern Hamesh Koreb region.
UN troops have since been deployed to the region.
The peace talks - the first between the Eastern Front and Khartoum - were initially due to have taken place last November but have been postponed several times since and had been set to begin on Tuesday in the Libyan capital.
Like their rebel counterparts in Darfur, the Eastern Front complains of marginalisation by the government in Khartoum, which it accuses of exploiting natural resources such as oil, natural gas, gold and other minerals at the expense of the local population.
The Eastern Front was founded by eastern Sudan's two main rebel groups, the Beja Congress and the Free Lions, early last year and claimed to have launched its first offensive against government positions in the Red Sea state last June.
An influential policy group said last month that simmering tensions in east Sudan were a "powder keg" that could explode into a major war, damaging peace efforts in Darfur and last year's north-south peace deal.
The International Crisis Group called on the Sudan People's Liberation Movement, which is now part of a power-sharing government in Khartoum, to urge Sudan's leadership to negotiate in good faith with the Eastern Front.