South Sudan's independence vote cleared two major hurdles on Wednesday after former U.S. president Jimmy Carter gave the poll his endorsement and organisers said huge turnouts meant the result would be binding.

Southerners are widely expected to choose to declare independence from the north in the week-long poll that entered its fifth day on Thursday -- a plebiscite promised in a 2005 peace deal that ended decades of north-south civil war.

Carter, who is leading one of the biggest teams observing the vote, told journalists: I believe it will meet international standards on the conduct of the process and also the freedom with which people have cast their votes.

We have two more days to go obviously but I don't think there is any doubt the results will be accepted without serious challenge, he added.

Carter told journalists on Thursday he also believed that international creditors should forgive most if not all of Sudan's crippling debt, to give both north and south access to fresh funds to cope with the shock of separation.

The vote's organising commission on Thursday said the vote's turnout had passed the 60 percent minimum needed to make the result binding, confirming its earlier forecasts.

The announcements came as Arab nomads and southern tribespeople, who have been caught up in border clashes since Friday, marring the poll, said they had reached a series of agreements.

The streets of Juba were calm on Wednesday, in contrast to the jubilant celebrations that greeted the start of the poll. But southerners were quietly satisfied with the progress.

Now that the vote is valid, it means the north's reaction is the only thing we don't know. Their reaction to separation is the only unknown left, said Martin Yokey, 39.

Many northerners are angry about the referendum, which looks likely to deprive them of a quarter of the territory in Africa's largest country and most of its known oil reserves.

Students clashed with police in north Sudan for the second day on Thursday in a rare public protest over price rises, sparked by an economic crisis that has been exacerbated by fears of the economic impact of the south's secession.

DEBT BURDEN

Northern and southern leaders remain at loggerheads over the position of their shared border and how they would share out oil revenues and debts after a split.

My belief (is) that a substantial portion -- perhaps all -- (of) existing debt should be forgiven because both the north and south need to have a net inflow of funds in the future to make it possible for them to sustain the shock that will come from separating the two nations, Carter said.

There is about $38 maybe $39 billion ( 23.97 to 24 billion pounds) dollars debt now and the World Bank tells us about $30 billion (18 billion pounds) of that is in arrears. That is a very serious burden of debt. I have a list of the creditors to whom the debt is owed and can't see anybody on the list who can't afford to forgive it.

Aid groups said thousands of south Sudanese trying to get home for the poll had been left stranded and dependent on food aid in the north after logistical problems and attacks in border areas blocked their route.

Fighting has followed increasing friction over the unresolved status of the fertile and oil-producing central region of Abyei, claimed by both Arab Misseriya nomads and the Dinka Ngok people, who are associated with the south.

At least 46 people have been killed since Friday, according to reports from both sides.

Kuol Deng Kuol, Paramount Chief of Dinka Ngok told Reuters both sides met on Wednesday and Thursday and agreed to pay each other blood money for 2010 clashes, to protect the safety of returnees and to allow the nomads to begin their southward migration with their livestock.

More than 600 southerners were stuck in Kadugli, the capital of Southern Kordofan state, which surrounds Abyei, after armed men attacked parts of their convoy on Monday, said an official from the International Organisation for Migration (IOM).

Preliminary results of the referendum are to be announced at the start of February, with official results two weeks later.

Sudan Sudan