Sudan’s parliament has passed a key law paving the way for a referendum on independence for the oil-rich south
The move ends months of wrangling between the north and south about how the referendum should be conducted.
Last week, southern politicians walked out of parliament in a row over where southerners would be able to vote.
The referendum, scheduled for January 2011, is a crucial part of the peace deal signed nearly five years ago which ended two decades of civil war.
The 2005 peace agreement saw President Omar al-Bashir’s northern National Congress Party (NCP) going into government with former Sudan People’s Liberation Movement (SPLM) rebels from the south.
It i widely predicted that the south will vote for independence but there are concerns that tensions will increase in the run-up to the referendum and a general election in April.
Mr Bashir and SPLM leader Salva Kiir reached a deal on the referendum earlier this month in crisis talks that followed angry demonstrations by southerners about electoral reforms.
But when northern politicians tried to amend a section of the referendum bill about where people could vote last week, southern MPs walked out of parliament.
This prompted the United States to put pressure on the NCP.
The law passed on Tuesday now stipulates that southerners living in the north will be allowed to vote there if they were born after 1956 but those born before that date will have to register and vote in the south.
The SPLM had feared the north would manipulate the vote if southerners who had not lived in southern Sudan since independence in 1956 had been allowed to vote anywhere.
“Anybody can claim: yes I have my grandparents from the south… unless you go and verify yourself in southern Sudan, this can be abused,” SPLM MP Aligu Manawa told the BBC’s Focus on Africa programme.
BBC Africa analyst Mary Harper says Sudan’s politicians try – in public at least – to talk of enduring unity and good relations between the north and south.
But they sometimes slip up and Mr Kiir recently warned southerners that if they voted against independence they would become second-class citizens in their own country, she says.
There are also problems regarding the border between the north and south, as the status of some areas has not yet been clearly defined.
And there are serious tensions in southern Sudan, with different ethnic groups fighting over land.
More than 2,000 people have been killed and 250,000 people displaced this year alone.
The 22-year war between the mainly Muslim north and the Christian and animist south claimed the lives of some 1.5 million people.

A German scientific team gave details of encryption to protect the public in debates over 4 billion mobile phone users.
Karsten Nohl, cooperation with other experts, has spent the last five months, cracking algorithm for encryption technology called GSM.
GSM is the most popular standard for mobile networks worldwide.
The project will listen to anyone – including criminals – in private telephone conversations.
Mr Nohl said the Chaos Communication Congress in Berlin that the project has shown that the GSM security was inadequate .
We try to inform people about the general weakness, he told the BBC.
We expect some additional pressure and customer demand for better encryption to create. The GSM Association (GSMA), which developed the algorithm, and oversees the development of standards, said Nohl project is totally illegal in the United Kingdom and many other countries.
This is not something we take lightly at all, said the spokesman.
Mr. Nohl, told the BBC that he consulted with lawyers before publication, and believes the project was legal.
Mr. Nohl have published work with some dozens of others, the requirements for the material to crack the A5 / 1 algorithm, 22-year-old code from many sources.
The code is designed to force intercepted telephone conversations through mobile phones and base stations change frequencies quickly to a series of 80 channels for prevention.

Parliament of Sudan is an important law paves the way for a referendum on independence from oil-rich southThe circulating in recent months that ended fighting between North and South, as the referendum will take place.
Last week was the Southern politicians in the parliament in a series in the south, where they will be able to vote.
The referendum, scheduled for January 2011, an important part of the peace agreement was signed nearly five years before the end of two decades of civil war.
The 2005 peace agreement has been President Omar al-Bashir’s northern National Congress Party (NCP) to go to the Government for the release of (former Sudan People’s SPLM) rebels in the south.
The i generally expected that the south will vote for independence, but there is concern that tensions will increase before the referendum and general elections in April.
Mr. Bashir and SPLM leader Salva Kiir agreed on the referendum earlier this month in crisis talks after angry protests from the southern electoral reform.
But when politicians tried to northern part of the referendum bill as amended, where people could vote last week, went south, members of parliament.
This led the United States exerted pressure on the NCP.
The bill approved Tuesday is expected that the South living in the north, the possibility exists, voting rights, if born after 1956, but those born before that date, you should register to vote south.
The SPLM had fear in northern manipulate votes in the south who had lived in southern Sudan since independence in 1956, if allowed to vote anywhere.
Everybody can say I have my grandparents, from the south … if you go and check yourself in southern Sudan, which can be misused, Manawa Aliu SPLM MPs told the BBC on Focus Africa Program.
BBC Africa analyst Mary Harper says that politicians try to Sudan – at least in public support – the talk of unity and good relations between North and South.
But sometimes I’m wrong and Mr Kiir warned recently, Southerners, if he voted against independence, were second-class citizens in their country, he said.
There are also problems in the border area between North and South, as the situation is not clearly defined in some areas.
And there are serious tensions in southern Sudan, with different ethnic groups in the land dispute.
More than 2,000 people died and 250,000 people displaced this year alone.
The 22-year war between the Muslim north and Christian and animist south has killed about 1.5 million people.

Two gay men arrested in Malawi after getting engaged are to be charged with gross public indecency, police say.
“We arrested them because they committed an offence; homosexuality in Malawi is illegal,” police spokesman Davie Chingwalu told the BBC.
Tiwonge Chimbalanga and Steven Monjeza held a traditional engagement ceremony over the weekend – believed to be the first gay couple in Malawi to do so.
Homosexuality carries a maximum prison sentence of 14 years in Malawi.
The pair are being held in separate cells in Blantyre until their case is heard, Mr Chingwalu told the BBC’s Network Africa programme.
The BBC’s Raphael Tenthani in Blantyre says the pair have been seen relaxing at the police station with Mr Tiwonge still wearing the dress he wore at the engagement party.
He says they may have to spend a few more nights in jail as the judiciary is on its Christmas recess and they will not be able to appear in court until next Monday.
Our correspondent says Malawi is a deeply conservative society, but recently a group of campaigners came together to form a gay rights organisation, Centre for the Development of People (CEDEP).
CEDEP’s executive director, Gift Trapence, says the laws used to arrest the couple are invalid because they are against the Bill of Rights enshrined in the 1995 constitution.
“Even if you arrest them or charge them for 20 years, you cannot change their sexual orientation. They are what they are,” he told the BBC.
“So the issue is in a democratic era – if you are arresting people based on their sexual orientation, are you doing justice to the fundamental human rights of these individuals?” he said.
Correspondents say some voices in government have also started to call for more openness about homosexuality as the authorities try to tackle high rates of HIV/Aids.

Committing a young woman died and her mother was seriously injured when a gunman shot them both before committing suicide.
The four-year-old woman was found with serious head injuries after neighbors alerted the police, a domestic dispute in Aldershot, Hampshire.
Although they urgently needed medical treatment, she died at the scene. The man was also killed in the incident came shortly after 1000 GMT, the.
Relationship of man with the child and the woman is not yet clear.
Police were the property of the Church Hill in 1011 GMT from neighbors about a national dispute involved called.
She was taken to hospital by Air Ambulance Surrey, where he remains included in a critical condition, police said.
A spokesman for Hampshire Police said a gun found in the property.
He said the incident was domestic and the police did not try someone else.
A large cordon was established around the end of the terrace house next to the main street of the city.
Officials also cut off access to Aldershot Manor Park, opposite the property.
Scenes of crime officers were seen entering the house, erected a small tent on the sidewalk.
Bouquets of flowers left in the house where the officers of the guard.

Nokia has ramped up its legal fight against Apple, arguing that almost all of its products infringe Nokia patents.
Nokia, the world’s largest phone maker, filed its new complaint with the US International Trade Commission (ITC).
The Finnish phone maker alleges that Apple is using patented technologies to “create key features in its products”, including iPods and iPhones.
In October Nokia sued Apple, saying that the company’s popular touchscreen iPhone infringed 10 of its patents.
Apple told the BBC that it would not comment on Nokia latest legal move.
However, the US firm recently countered by filing its own lawsuit against Nokia, saying the phone maker had copied certain aspects of the iPhone and infringed 13 of its patents.
The new complaint to the ITC relates to seven patents related to “user interface, as well as camera, antenna and power management technologies”.
Nokia told Reuters that the firm expected the ITC to decide whether to pursue the case in around 30 days.