|Southerners may opt for secession but the ruling NCP has been campaigning for unity ahead of the referendum [AFP]
North Sudan's dominant party has threatened to reject the results of a southern independence referendum unless the south withdraws its troops from disputed areas and allows free campaigning in the vote.
Southerners are just over 100 days away from a vote on whether to stay part of Sudan or declare independence.
Haj Majid Suwar, a senior member of the ruling National Congress Party (NCP), said "we may not recognise the results [of the referendum]" in answer to reporters' questions as to what the NCP would do if southerners did not allow open campaigning and did not move their troops.
"Maybe we will talk to ... the USA and the UN and the AU (African Union) and say that the other side [the Sudan People's Liberation Movement] didn't fulfil the CPA [Comprehensive Peace Agreement]," Suwar, who is also Sudan's youth and sports minister, said on Monday.
The referendum was promised by the agreement, which was signed in 2005, ending decades of the north-south civil war.
Under the agreement, the south formed its own government, which has limited autonomy and in which the north has a small representation. South Sudan is nominally represented in the government of national unity, which is led by the Khartoum-based NCP.
Suwar said basic freedoms in the south had been compromised and many people had been arrested and some killed.
"There is no freedom of [speech] in the south or for any movement to speak out for unity. Many people have been arrested and some of them were even killed," he said.
"There is no freedom of (speech) in the south or for any movement to speak out for unity. Many people have been arrested and some of them were even killed"
Haj Majid Suwar, senior member of the National Congress Party (NCP)
The southern army dismissed the accusations, saying all its troops are inside south Sudan and none of its solders have done anything to stop or harass unity campaigners.
"What he is saying is baseless. It is a statement of an occupier who wants to occupy more land," Kuol Deim Kuol, a spokesman for the Sudan People's Liberation Army (SPLA), the southern government force, said.
The prospect of a contested referendum result will dismay analysts who have warned that north and south Sudan could go back to war if the vote is disrupted.
Last week, Ban Ki-moon, the UN secretary-general, cautioned Sudan that the two self-determination votes, which could see the break-up of Africa's biggest nation, must be "peaceful" and "free of intimidation".
In addition to the referendum on the south's independence, a small region called Abyei, which sits astride the oil-rich border between south and north sudan, will vote on whether it should belong to south Sudan or north Sudan.
In his statements on Monday, Suwar, the Sudanese minister, also accused the southern army of moving into areas close to the northern states of White Nile and Southern Kordofan, near Abyei.
The troop movements and the crackdown on unity supporters threatened the validity of the vote because they broke the terms of the peace agreement and Sudan's southern referendum act, he said.
Suwar said the validity of the referendum also depended on international donors fulfilling promises to fund the referendum and said world powers needed to remain impartial about the outcome of the vote.
The NCP has accused Southern Sudan's governing SPLM of campaigning for separation - as opposed to unity - while the SPLM accuses the NCP of trying to disrupt the referendum to keep control of the territory's oil.
Omar al-Bashir, Sudan's president, and the NCP say they are campaigning to persuade southerners to choose unity.
Both parties strengthened their hold on their respective halves of the country in April elections. But observers said that the election was marred by widespread irregularities, disorganisation and intimidation of minority voices.
Meanwhile, a governor in south Sudan has said that a local militia will be armed and supplied with funds in order to defend local villages. The militia - known as the Arrow Boys - has previously fought Uganda's Lord's Resistance Army.
Reporting from Juba in southern Sudan, Al Jazeera's Haru Mutasa said that the SPLA does not have the manpower or weapons to patrol and protect southern Sudan, where many live in remote areas, in rough terrain, where the SPLA have been unable to defeat the LRA.
Our correspondent said arming the militia was "good news" to the villagers in the region who "feel that the Arrow Boys have protected them for years. They believe that the SPLA has failed in doing that, and they feel safer with these Arrow Boys".