South Sudan's independence referendum was credible and well organised, European observers said in their first official judgment on the poll on Monday, moving the region a step closer to secession.

Early results from the week-long vote suggest an overwhelming vote to split away from the mostly Muslim north after decades of civil war.
"The European Union election observation mission assess the voting process of the Southern Sudan Referendum credible and well-organised in a mostly peaceful environment," a preliminary statement seen by Reuters said.

Organisers have reported turnouts of over 90 percent of voters in some parts of the oil-producing south. In the capital Juba six centres had more than 2,500 votes for secession compared to a maximum of just 25 votes for unity.

Preliminary results are expected by the end of the month and south Sudan would become an independent nation on July 9, according to the terms of the 2005 north-south peace deal that promised the referendum.

Senior north Sudanese official Ibrahim Ghandour told Reuters last week the voting, which ended on Saturday, had been "broadly fair", allaying fears that disagreements over the outcome would reignite conflict.

Former U.S. President Jimmy Carter, leading the other major observation mission, last week said the south was highly likely to vote for secession and that the process had largely met international standards.

His Carter Center observer mission was due to give a preliminary statement on the referendum later on Monday.