He told the BBC he was pleased with President Omar al-Bashir acceptance of the referendum. He said the vote will allow the people of South Sudan to decide their own future for the first time since 1898.

On his final visit to the south before the referendum, Bashir said that he would be sad to see Sudan split in two. But he added he would be happy if that brought "real peace" to both sides.

Analysts said President Bashir's remarks reflect a growing realisation by the Sudanese government that it cannot prevent the week-long referendum.

The vote is part of a 2005 deal that ended a two-decades-long war.

"We are pleased at the end of the day, despite difficulties and challenges, President Bashir had to realise that this agreement is not just between the Sudanese alone but it involves the whole international community," said Dr Benjamin.

However, a referendum on independence for south Sudan on Sunday raises tough questions about the legitimacy of Africa's colonial borders and sets a precedent for existing secessionist movements, analysts say.

"There is an uneasiness in Africa towards this independence because it breaks with a tradition (of borders being inviolable) and because it seems to be taking place under US pressure," says Roland Marchal, Sudan specialist and senior researcher at the Institute of Political Sciences in Paris.

"This is seen as if it were a Berlin II, with the colonial powers carving up Africa again," he said, referring to the 1885 Berlin Conference where European powers divided and colonised Africa among themselves.

A peace accord in 2005 between the mostly Arab Muslim north and the largely Christian African south ended a 22-year civil war in Sudan, with an agreement that southerners could vote for independence after six years.

Southern Sudan has been marginalised by a succession of governments in Khartoum, from colonial times onwards.

The north and south are also divided by culture, religion, ethnicity and a history of conflict, correspondents say.

For the vote to be considered valid, 60% of voters must take part.

Darfur's most active group, the Justice and Equality Movement, said in August that it would demand self-determination if it’s nearly eight-year conflict with the government continued.