Sudan seen massing troops in oil state, U.N. staff blocked
South Sudan to secede on Saturday but oil state conflict threatens stability after split
Sudan's division echoes in war-ravaged Darfur
Many fear south Sudan's split will worsen fighting in the war-torn Darfur region
Southern party warns of civil war over border tensions
Fighting may spread to the north's Blue Nile and Darfur regions, SPLM says
UN faces big challenge as Sudan readies for split
The south is scarred by decades of civil war, tribal conflicts and poverty
FACTBOX-Independence of South Sudan on July 9
The steps to statehood