Darfuris began voting on Monday in a referendum on whether to reunite the states of their arid western region into one entity, a poll that Sudan says will settle a contentious issue at the heart of the long-running conflict.
The Sudanese government's decision to split Darfur into three states in 1994 helped fuel discontent that erupted into fighting in 2003 - rebels and many from the large Fur tribe said the break-up allowed Khartoum to divide and rule them.
Sudan, which later split Darfur further into five states, has presented this week's vote as a major concession. But rebel and opposition groups have again cried foul, saying the vote will be rigged and calling on their supporters to boycott it.
Students inside El Fasher University, in the government-controlled capital of North Darfur state, protested against the vote and witnesses said similar rallies took place in at least three refugee camps in Central Darfur state.