Troops from north and south Sudan have begun deploying to the disputed Abyei oil region to secure the area after recent fighting raised fears of a new civil war.

The first soldiers of a 600-strong force made up jointly of the former southern rebel group, the Sudan People's Liberation Army, and the northern Sudanese army began arriving in the region Wednesday.

The troops were deployed after Abyei town was nearly destroyed last month by clashes between forces from Sudan's northern-based government and semi-autonomous south.

The two sides are working to preserve a 2005 peace deal that ended Sudan's 21-year north-south civil war.

In another development, Sudan has opened the trials of 39 Darfur rebels facing terrorism charges for their alleged role in a rebel attack on the capital, Khartoum and its suburb, Omdurman, last month.

They could face the death penalty if convicted.

The rebel Justice and Equality Movement launched the attack May 10 after crossing hundreds of kilometers of desert. It was the closest rebels from the western Darfur region have come to the capital. At least 200 people died in the violence.

Human Rights Watch urged Sudan's government Wednesday to release or charge the hundreds of Darfuris who have been arrested since last month's attack. The New York-based group said prisoners have complained of mistreatment and torture.

Also Wednesday, the joint United Nations-African Union mission in Darfur says one of its staffers was assaulted and briefly abducted by Arab militia. It said three other staff members were held at gunpoint. U.N. forces refrained from opening fire, and a Sudanese soldier intervened to end the standoff.

Some information for this report was provided by AFP, AP and Reuters.