However, the missions' preliminary statements also noted shortcomings, including insufficient voter education, pre-polling campaigning overshadowing discussions about post-referendum arrangements and some logistics issues.

The Carter Center, with over 100 observers on the ground during polling, declared Southern Sudan's self-determination referendum credible and "broadly consistent with international standards".

"It appears virtually certain that the results will be in favour of secession," added the centre's statement issued today, based on early reports of vote counting results.

The same observer mission also noted some shortcomings in the process, including the absence of large-scale and unbiased voter education, overwhelming presence of security at polling centres and uneven application of voter eligibility criteria, especially in North Sudan.

While calling the referendum credible and "a remarkable operational and political achievement", the European Union (EU) observation mission's statement today also mentioned a lack of post-referendum discussions during the campaign period.

"(The) debate on the consequences of secession or the continued unity of Sudan was drowned out," the EU mission stated.

Commitments made in the 2005 Abyei Protocol and the 2009 Abyei Area Referendum Act to hold a referendum for the oil-rich area bordering northern and southern Sudan were not met, the EU observers noted, adding that this was "partially responsible for subsequent violence and instability in the Abyei region".

The statement of the National Elections Observation Network remarked on several shortcomings, witnessed by some of the network's 300 observers deployed across Sudan during referendum registration and polling.

Some registration centres ran out of registration cards, the statement read, while bemoaning a weak civic education process, negligible role of civil society in the referendum, and occasional irregularities, including polling staff voting on behalf of voters.

Overall, the observer missions commended the Southern Sudan Referendum Commission and its counterparts for successful implementation of the referendum despite short timelines and logistical challenges, and recognized the critical role played by the UN Integrated Referendum and Elections Division as well as other international partners.