Southerners are just over 100 days away from a vote on whether to stay part of Sudan or declare independence. The plebiscite was promised in the 2005 Comprehensive Peace Agreement (CPA) that ended decades of north-south civil war.

Coming so close to the scheduled referendum date, the statement by a minister from President Omar Hassan Al-Bashir's National Congress Party (NCP) will dismay observers already worried Sudan is running out of time to stage the vote.

The minister accused the south's army of straying out of areas assigned to them in the peace accord, and said southern authorities were cracking down on supporters of Sudanese unity.

"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, Sudan's youth and sports minister and a senior NCP member, told reporters.

Asked what the NCP would do if the southerners did not allow open campaigning and move their troops, he answered: "Maybe we will talk to ... the USA and the UN and the AU (African Union) and say that the other side, they didn't fulfil the CPA, so we may not recognize the results."

Analysts say most people from the oil-producing south want independence.

The minister also called on international donors to fulfil promises to fund the referendum and said world powers needed to remain impartial about the outcome of the vote.