Sudan's northern-based government says it will not accept the results of an upcoming independence referendum in the south unless the vote is free and southern military forces withdraw from disputed areas.
Senior ruling party official Rabie Abdelati Obeid said on Tuesday that no one in the south should interfere with people campaigning for the unity of the country.
The National Congress Party official says a failure of southern Sudan's autonomous government to follow this guideline will invalidate the January 9 referendum.
On Monday, Sudanese Youth and Sports Minister Haj Majid Suwar said southern Sudanese military forces also must withdraw from areas north of Sudan's disputed north-south border before the referendum.
Both sides accuse each other of massing troops along the border, much of which is undefined.
Southern Sudan's main party accuses the NCP of trying to undermine the referendum to delay a secession of the oil-rich southern half of the country.
The former rebel Sudan People's Liberation Movement says the northern-based government is monopolizing state broadcasting to prevent supporters of secession from airing their views. NCP official Obeid denies the accusation.
Sudan's government also has fallen behind in its preparations for the referendum. Sudanese election commission chairman Mohammed Ibrahim Khalil told Reuters on Tuesday the registration of voters is likely to start three weeks later than planned in November.
He says the delay is needed to allow election workers to deliver forms to 3,600 voter registration centers.
U.S. election monitoring group The Carter Center said Tuesday Sudan must also approve the election commission's budget, recruit and train referendum workers, and publish a detailed referendum calendar.
The group has sent 16 people to Sudan to observe referendum preparations.
Many analysts predict southerners, who hold predominantly Christian and traditional beliefs, will choose independence from the Muslim-dominated northern government.
The Sudanese government agreed to hold the referendum as part of 2005 peace deal that ended two decades of civil war with the south.
Some information for this report was provided by AP and Reuters.