Five South Sudan states have registered more voters than official census figures say could live there. One, Unity state, signed up more than 200 percent of its official eligible population.
An official from the North's ruling National Congress Party told Reuters the numbers show the voter registration process in the South is marred with major fraud.
But officials from the South's Sudan People's Liberation Movement have long maintained the national census that calculated the semi-autonomous region's population was "rigged." The census data is critical because it determines the number of seats up for election in the next parliament.
In a recent interview in Juba, the top SPLM official in the South, Anne Itto, told VOA her party would reject parliamentary elections in April based upon the official data, which could drop the South's representation in the body by nearly a third.
"Legislative elections would use the census results, and we feel it is full of flaws. And now registration itself is showing that there must have been a mistake," she said.
Itto suggested that SPLM would accept elections on the national and southern presidencies as well as the governorships, but added the likely-inflammatory suggestion that elections be postponed until after its independence referendum if an acceptable agreement could not be reached.
"Either have executive elections or we will defer the elections until the referendum, unless of course there are some other arrangements that would increase the number of southern Sudanese to raise their percentage of South Sudan in the national assembly to 30 percent or so," she added.
The Sudanese constitution can be legally amended with a two-thirds vote in parliament. Southerners fear if its portion of seats drops to only 20 percent, as could take place under current election law, the northern parties could unite to take away its prized independence vote, now scheduled for January 2011.
The debate over the registration figures stands in stark contrast to the concerns expressed by many southerners and outside observers at the beginning of the registration drive that poor infrastructure and lack of resources would likely doom the process.
Registration across the South started poorly, but by mid-November it had become apparent the initial predictions of extremely low turnout were premature.
According to southern election officials, the voter drive began gaining steam after the South Sudanese president and SPLM chair Salva Kiir began seriously mobilizing public sentiment and the party apparatus towards getting southerners to sign up.
Southern Sudan fought a decades-long civil war against the ruling Khartoum government. A 2005 landmark peace agreement gave the South a share of national power as well as its own semi-autonomous government.
The deal initiated a six-year interim governing period, during which national elections would be followed up by a southern independence referendum. A number of recent reports have warned the political situation between North and South is deteriorating towards renewed armed conflict.