Sudan as part of a 2005 comprehensive peace agreement votes in January to break into northern and southern states. Members of the U.N. Security Council welcomed the Monday start to the voter registration for the effort.
Benjamin Mkapa, a Tanzanian diplomat and head of a three-member U.N. panel on Sudan, said he was concerned the turnout for the voter registration was low.
"In the north, turnout remains extremely low," he was quoted by the United Nations' news agency as saying. "Many southern Sudanese appear uninterested or unwilling to register."
U.N. delegates during a recent debate at the General Assembly for funding for the U.N. mission in Sudan said the implications of the January measure would have wide-reaching effects.
Grum Abay, the Ethiopian envoy to the United Nations, said he felt the referendum would "reverberate across Africa."
Mkapa said it was imperative that all parties in the north and south publicize the January measure.
U.S. Secretary of State Hillary Clinton said last week that Washington was keen to make sure the process went forward with Sudan's independence in mind, adding the comprehensive peace agreement is ultimately in the hands of Sudanese authorities.