The deployment of an international force to southern Sudan could be delayed by a dispute over which countries send peacekeeping troops.
SPLA leader John Garang is expected in Rumbek soon
The southern rebel group is unhappy that too many Muslim countries have been asked, a senior UN source says.
The UN is hoping to deploy in March some 10,000 troops to monitor the peace deal between the Islamic government and Christian and Animist rebels.
The deal ended 21 years of war which left some 1.5m people dead.
A key member of the rebel SPLM, Deng Alour Deng, said they had not been consulted over which countries would make up the new peace mission to southern Sudan and that they had reservations about the whole list.
The BBC's Jonah Fisher in the southern capital, Rumbek, says that several countries are thought to have been approached, including Pakistan, Bangladesh and Malaysia.
A Security Council vote on the UN mission is not due until early February but in order to begin arriving in March participating countries need to be planning ahead now, our correspondent says.
On Thursday, the first diplomatic mission was opened in Rumbek, 900km south of the capital, Khartoum, to represent Dutch and British interests.
Speaking on his first visit to Rumbek, UN envoy Jan Pronk said this week that the challenge to secure peace and develop the south was huge.
Rumbek has no paved roads or multi-storey buildings and hardly any running water or electricity.